| // ignore-tidy-filelength |
| // This file almost exclusively consists of the definition of `Iterator`. We |
| // can't split that into multiple files. |
| |
| use crate::cmp::{self, Ordering}; |
| use crate::ops::{Add, Try}; |
| |
| use super::super::LoopState; |
| use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse}; |
| use super::super::{FlatMap, Flatten}; |
| use super::super::{FromIterator, Product, Sum, Zip}; |
| use super::super::{ |
| Inspect, Map, MapWhile, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, |
| }; |
| |
| fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {} |
| |
| /// An interface for dealing with iterators. |
| /// |
| /// This is the main iterator trait. For more about the concept of iterators |
| /// generally, please see the [module-level documentation]. In particular, you |
| /// may want to know how to [implement `Iterator`][impl]. |
| /// |
| /// [module-level documentation]: index.html |
| /// [impl]: index.html#implementing-iterator |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_on_unimplemented( |
| on( |
| _Self = "[std::ops::Range<Idx>; 1]", |
| label = "if you meant to iterate between two values, remove the square brackets", |
| note = "`[start..end]` is an array of one `Range`; you might have meant to have a `Range` \ |
| without the brackets: `start..end`" |
| ), |
| on( |
| _Self = "[std::ops::RangeFrom<Idx>; 1]", |
| label = "if you meant to iterate from a value onwards, remove the square brackets", |
| note = "`[start..]` is an array of one `RangeFrom`; you might have meant to have a \ |
| `RangeFrom` without the brackets: `start..`, keeping in mind that iterating over an \ |
| unbounded iterator will run forever unless you `break` or `return` from within the \ |
| loop" |
| ), |
| on( |
| _Self = "[std::ops::RangeTo<Idx>; 1]", |
| label = "if you meant to iterate until a value, remove the square brackets and add a \ |
| starting value", |
| note = "`[..end]` is an array of one `RangeTo`; you might have meant to have a bounded \ |
| `Range` without the brackets: `0..end`" |
| ), |
| on( |
| _Self = "[std::ops::RangeInclusive<Idx>; 1]", |
| label = "if you meant to iterate between two values, remove the square brackets", |
| note = "`[start..=end]` is an array of one `RangeInclusive`; you might have meant to have a \ |
| `RangeInclusive` without the brackets: `start..=end`" |
| ), |
| on( |
| _Self = "[std::ops::RangeToInclusive<Idx>; 1]", |
| label = "if you meant to iterate until a value (including it), remove the square brackets \ |
| and add a starting value", |
| note = "`[..=end]` is an array of one `RangeToInclusive`; you might have meant to have a \ |
| bounded `RangeInclusive` without the brackets: `0..=end`" |
| ), |
| on( |
| _Self = "std::ops::RangeTo<Idx>", |
| label = "if you meant to iterate until a value, add a starting value", |
| note = "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \ |
| bounded `Range`: `0..end`" |
| ), |
| on( |
| _Self = "std::ops::RangeToInclusive<Idx>", |
| label = "if you meant to iterate until a value (including it), add a starting value", |
| note = "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \ |
| to have a bounded `RangeInclusive`: `0..=end`" |
| ), |
| on( |
| _Self = "&str", |
| label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" |
| ), |
| on( |
| _Self = "std::string::String", |
| label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" |
| ), |
| on( |
| _Self = "[]", |
| label = "borrow the array with `&` or call `.iter()` on it to iterate over it", |
| note = "arrays are not iterators, but slices like the following are: `&[1, 2, 3]`" |
| ), |
| on( |
| _Self = "{integral}", |
| note = "if you want to iterate between `start` until a value `end`, use the exclusive range \ |
| syntax `start..end` or the inclusive range syntax `start..=end`" |
| ), |
| label = "`{Self}` is not an iterator", |
| message = "`{Self}` is not an iterator" |
| )] |
| #[must_use = "iterators are lazy and do nothing unless consumed"] |
| pub trait Iterator { |
| /// The type of the elements being iterated over. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| type Item; |
| |
| /// Advances the iterator and returns the next value. |
| /// |
| /// Returns [`None`] when iteration is finished. Individual iterator |
| /// implementations may choose to resume iteration, and so calling `next()` |
| /// again may or may not eventually start returning [`Some(Item)`] again at some |
| /// point. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`Some(Item)`]: ../../std/option/enum.Option.html#variant.Some |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// // A call to next() returns the next value... |
| /// assert_eq!(Some(&1), iter.next()); |
| /// assert_eq!(Some(&2), iter.next()); |
| /// assert_eq!(Some(&3), iter.next()); |
| /// |
| /// // ... and then None once it's over. |
| /// assert_eq!(None, iter.next()); |
| /// |
| /// // More calls may or may not return `None`. Here, they always will. |
| /// assert_eq!(None, iter.next()); |
| /// assert_eq!(None, iter.next()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn next(&mut self) -> Option<Self::Item>; |
| |
| /// Returns the bounds on the remaining length of the iterator. |
| /// |
| /// Specifically, `size_hint()` returns a tuple where the first element |
| /// is the lower bound, and the second element is the upper bound. |
| /// |
| /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`. |
| /// A [`None`] here means that either there is no known upper bound, or the |
| /// upper bound is larger than [`usize`]. |
| /// |
| /// # Implementation notes |
| /// |
| /// It is not enforced that an iterator implementation yields the declared |
| /// number of elements. A buggy iterator may yield less than the lower bound |
| /// or more than the upper bound of elements. |
| /// |
| /// `size_hint()` is primarily intended to be used for optimizations such as |
| /// reserving space for the elements of the iterator, but must not be |
| /// trusted to e.g., omit bounds checks in unsafe code. An incorrect |
| /// implementation of `size_hint()` should not lead to memory safety |
| /// violations. |
| /// |
| /// That said, the implementation should provide a correct estimation, |
| /// because otherwise it would be a violation of the trait's protocol. |
| /// |
| /// The default implementation returns `(0, `[`None`]`)` which is correct for any |
| /// iterator. |
| /// |
| /// [`usize`]: ../../std/primitive.usize.html |
| /// [`Option`]: ../../std/option/enum.Option.html |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// let iter = a.iter(); |
| /// |
| /// assert_eq!((3, Some(3)), iter.size_hint()); |
| /// ``` |
| /// |
| /// A more complex example: |
| /// |
| /// ``` |
| /// // The even numbers from zero to ten. |
| /// let iter = (0..10).filter(|x| x % 2 == 0); |
| /// |
| /// // We might iterate from zero to ten times. Knowing that it's five |
| /// // exactly wouldn't be possible without executing filter(). |
| /// assert_eq!((0, Some(10)), iter.size_hint()); |
| /// |
| /// // Let's add five more numbers with chain() |
| /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); |
| /// |
| /// // now both bounds are increased by five |
| /// assert_eq!((5, Some(15)), iter.size_hint()); |
| /// ``` |
| /// |
| /// Returning `None` for an upper bound: |
| /// |
| /// ``` |
| /// // an infinite iterator has no upper bound |
| /// // and the maximum possible lower bound |
| /// let iter = 0..; |
| /// |
| /// assert_eq!((usize::MAX, None), iter.size_hint()); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| (0, None) |
| } |
| |
| /// Consumes the iterator, counting the number of iterations and returning it. |
| /// |
| /// This method will call [`next`] repeatedly until [`None`] is encountered, |
| /// returning the number of times it saw [`Some`]. Note that [`next`] has to be |
| /// called at least once even if the iterator does not have any elements. |
| /// |
| /// [`next`]: #tymethod.next |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`Some`]: ../../std/option/enum.Option.html#variant.Some |
| /// |
| /// # Overflow Behavior |
| /// |
| /// The method does no guarding against overflows, so counting elements of |
| /// an iterator with more than [`usize::MAX`] elements either produces the |
| /// wrong result or panics. If debug assertions are enabled, a panic is |
| /// guaranteed. |
| /// |
| /// # Panics |
| /// |
| /// This function might panic if the iterator has more than [`usize::MAX`] |
| /// elements. |
| /// |
| /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// assert_eq!(a.iter().count(), 3); |
| /// |
| /// let a = [1, 2, 3, 4, 5]; |
| /// assert_eq!(a.iter().count(), 5); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn count(self) -> usize |
| where |
| Self: Sized, |
| { |
| #[inline] |
| fn add1<T>(count: usize, _: T) -> usize { |
| // Might overflow. |
| Add::add(count, 1) |
| } |
| |
| self.fold(0, add1) |
| } |
| |
| /// Consumes the iterator, returning the last element. |
| /// |
| /// This method will evaluate the iterator until it returns [`None`]. While |
| /// doing so, it keeps track of the current element. After [`None`] is |
| /// returned, `last()` will then return the last element it saw. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// assert_eq!(a.iter().last(), Some(&3)); |
| /// |
| /// let a = [1, 2, 3, 4, 5]; |
| /// assert_eq!(a.iter().last(), Some(&5)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn last(self) -> Option<Self::Item> |
| where |
| Self: Sized, |
| { |
| #[inline] |
| fn some<T>(_: Option<T>, x: T) -> Option<T> { |
| Some(x) |
| } |
| |
| self.fold(None, some) |
| } |
| |
| /// Returns the `n`th element of the iterator. |
| /// |
| /// Like most indexing operations, the count starts from zero, so `nth(0)` |
| /// returns the first value, `nth(1)` the second, and so on. |
| /// |
| /// Note that all preceding elements, as well as the returned element, will be |
| /// consumed from the iterator. That means that the preceding elements will be |
| /// discarded, and also that calling `nth(0)` multiple times on the same iterator |
| /// will return different elements. |
| /// |
| /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the |
| /// iterator. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// assert_eq!(a.iter().nth(1), Some(&2)); |
| /// ``` |
| /// |
| /// Calling `nth()` multiple times doesn't rewind the iterator: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert_eq!(iter.nth(1), Some(&2)); |
| /// assert_eq!(iter.nth(1), None); |
| /// ``` |
| /// |
| /// Returning `None` if there are less than `n + 1` elements: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// assert_eq!(a.iter().nth(10), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn nth(&mut self, mut n: usize) -> Option<Self::Item> { |
| while let Some(x) = self.next() { |
| if n == 0 { |
| return Some(x); |
| } |
| n -= 1; |
| } |
| None |
| } |
| |
| /// Creates an iterator starting at the same point, but stepping by |
| /// the given amount at each iteration. |
| /// |
| /// Note 1: The first element of the iterator will always be returned, |
| /// regardless of the step given. |
| /// |
| /// Note 2: The time at which ignored elements are pulled is not fixed. |
| /// `StepBy` behaves like the sequence `next(), nth(step-1), nth(step-1), …`, |
| /// but is also free to behave like the sequence |
| /// `advance_n_and_return_first(step), advance_n_and_return_first(step), …` |
| /// Which way is used may change for some iterators for performance reasons. |
| /// The second way will advance the iterator earlier and may consume more items. |
| /// |
| /// `advance_n_and_return_first` is the equivalent of: |
| /// ``` |
| /// fn advance_n_and_return_first<I>(iter: &mut I, total_step: usize) -> Option<I::Item> |
| /// where |
| /// I: Iterator, |
| /// { |
| /// let next = iter.next(); |
| /// if total_step > 1 { |
| /// iter.nth(total_step-2); |
| /// } |
| /// next |
| /// } |
| /// ``` |
| /// |
| /// # Panics |
| /// |
| /// The method will panic if the given step is `0`. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [0, 1, 2, 3, 4, 5]; |
| /// let mut iter = a.iter().step_by(2); |
| /// |
| /// assert_eq!(iter.next(), Some(&0)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), Some(&4)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iterator_step_by", since = "1.28.0")] |
| fn step_by(self, step: usize) -> StepBy<Self> |
| where |
| Self: Sized, |
| { |
| StepBy::new(self, step) |
| } |
| |
| /// Takes two iterators and creates a new iterator over both in sequence. |
| /// |
| /// `chain()` will return a new iterator which will first iterate over |
| /// values from the first iterator and then over values from the second |
| /// iterator. |
| /// |
| /// In other words, it links two iterators together, in a chain. 🔗 |
| /// |
| /// [`once`] is commonly used to adapt a single value into a chain of |
| /// other kinds of iteration. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a1 = [1, 2, 3]; |
| /// let a2 = [4, 5, 6]; |
| /// |
| /// let mut iter = a1.iter().chain(a2.iter()); |
| /// |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// assert_eq!(iter.next(), Some(&4)); |
| /// assert_eq!(iter.next(), Some(&5)); |
| /// assert_eq!(iter.next(), Some(&6)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Since the argument to `chain()` uses [`IntoIterator`], we can pass |
| /// anything that can be converted into an [`Iterator`], not just an |
| /// [`Iterator`] itself. For example, slices (`&[T]`) implement |
| /// [`IntoIterator`], and so can be passed to `chain()` directly: |
| /// |
| /// ``` |
| /// let s1 = &[1, 2, 3]; |
| /// let s2 = &[4, 5, 6]; |
| /// |
| /// let mut iter = s1.iter().chain(s2); |
| /// |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// assert_eq!(iter.next(), Some(&4)); |
| /// assert_eq!(iter.next(), Some(&5)); |
| /// assert_eq!(iter.next(), Some(&6)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// If you work with Windows API, you may wish to convert [`OsStr`] to `Vec<u16>`: |
| /// |
| /// ``` |
| /// #[cfg(windows)] |
| /// fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> { |
| /// use std::os::windows::ffi::OsStrExt; |
| /// s.encode_wide().chain(std::iter::once(0)).collect() |
| /// } |
| /// ``` |
| /// |
| /// [`once`]: fn.once.html |
| /// [`Iterator`]: trait.Iterator.html |
| /// [`IntoIterator`]: trait.IntoIterator.html |
| /// [`OsStr`]: ../../std/ffi/struct.OsStr.html |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> |
| where |
| Self: Sized, |
| U: IntoIterator<Item = Self::Item>, |
| { |
| Chain::new(self, other.into_iter()) |
| } |
| |
| /// 'Zips up' two iterators into a single iterator of pairs. |
| /// |
| /// `zip()` returns a new iterator that will iterate over two other |
| /// iterators, returning a tuple where the first element comes from the |
| /// first iterator, and the second element comes from the second iterator. |
| /// |
| /// In other words, it zips two iterators together, into a single one. |
| /// |
| /// If either iterator returns [`None`], [`next`] from the zipped iterator |
| /// will return [`None`]. If the first iterator returns [`None`], `zip` will |
| /// short-circuit and `next` will not be called on the second iterator. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a1 = [1, 2, 3]; |
| /// let a2 = [4, 5, 6]; |
| /// |
| /// let mut iter = a1.iter().zip(a2.iter()); |
| /// |
| /// assert_eq!(iter.next(), Some((&1, &4))); |
| /// assert_eq!(iter.next(), Some((&2, &5))); |
| /// assert_eq!(iter.next(), Some((&3, &6))); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Since the argument to `zip()` uses [`IntoIterator`], we can pass |
| /// anything that can be converted into an [`Iterator`], not just an |
| /// [`Iterator`] itself. For example, slices (`&[T]`) implement |
| /// [`IntoIterator`], and so can be passed to `zip()` directly: |
| /// |
| /// [`IntoIterator`]: trait.IntoIterator.html |
| /// [`Iterator`]: trait.Iterator.html |
| /// |
| /// ``` |
| /// let s1 = &[1, 2, 3]; |
| /// let s2 = &[4, 5, 6]; |
| /// |
| /// let mut iter = s1.iter().zip(s2); |
| /// |
| /// assert_eq!(iter.next(), Some((&1, &4))); |
| /// assert_eq!(iter.next(), Some((&2, &5))); |
| /// assert_eq!(iter.next(), Some((&3, &6))); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// `zip()` is often used to zip an infinite iterator to a finite one. |
| /// This works because the finite iterator will eventually return [`None`], |
| /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: |
| /// |
| /// ``` |
| /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); |
| /// |
| /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); |
| /// |
| /// assert_eq!((0, 'f'), enumerate[0]); |
| /// assert_eq!((0, 'f'), zipper[0]); |
| /// |
| /// assert_eq!((1, 'o'), enumerate[1]); |
| /// assert_eq!((1, 'o'), zipper[1]); |
| /// |
| /// assert_eq!((2, 'o'), enumerate[2]); |
| /// assert_eq!((2, 'o'), zipper[2]); |
| /// ``` |
| /// |
| /// [`enumerate`]: trait.Iterator.html#method.enumerate |
| /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> |
| where |
| Self: Sized, |
| U: IntoIterator, |
| { |
| Zip::new(self, other.into_iter()) |
| } |
| |
| /// Takes a closure and creates an iterator which calls that closure on each |
| /// element. |
| /// |
| /// `map()` transforms one iterator into another, by means of its argument: |
| /// something that implements [`FnMut`]. It produces a new iterator which |
| /// calls this closure on each element of the original iterator. |
| /// |
| /// If you are good at thinking in types, you can think of `map()` like this: |
| /// If you have an iterator that gives you elements of some type `A`, and |
| /// you want an iterator of some other type `B`, you can use `map()`, |
| /// passing a closure that takes an `A` and returns a `B`. |
| /// |
| /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is |
| /// lazy, it is best used when you're already working with other iterators. |
| /// If you're doing some sort of looping for a side effect, it's considered |
| /// more idiomatic to use [`for`] than `map()`. |
| /// |
| /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
| /// [`FnMut`]: ../../std/ops/trait.FnMut.html |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter().map(|x| 2 * x); |
| /// |
| /// assert_eq!(iter.next(), Some(2)); |
| /// assert_eq!(iter.next(), Some(4)); |
| /// assert_eq!(iter.next(), Some(6)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// If you're doing some sort of side effect, prefer [`for`] to `map()`: |
| /// |
| /// ``` |
| /// # #![allow(unused_must_use)] |
| /// // don't do this: |
| /// (0..5).map(|x| println!("{}", x)); |
| /// |
| /// // it won't even execute, as it is lazy. Rust will warn you about this. |
| /// |
| /// // Instead, use for: |
| /// for x in 0..5 { |
| /// println!("{}", x); |
| /// } |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn map<B, F>(self, f: F) -> Map<Self, F> |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> B, |
| { |
| Map::new(self, f) |
| } |
| |
| /// Calls a closure on each element of an iterator. |
| /// |
| /// This is equivalent to using a [`for`] loop on the iterator, although |
| /// `break` and `continue` are not possible from a closure. It's generally |
| /// more idiomatic to use a `for` loop, but `for_each` may be more legible |
| /// when processing items at the end of longer iterator chains. In some |
| /// cases `for_each` may also be faster than a loop, because it will use |
| /// internal iteration on adaptors like `Chain`. |
| /// |
| /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::sync::mpsc::channel; |
| /// |
| /// let (tx, rx) = channel(); |
| /// (0..5).map(|x| x * 2 + 1) |
| /// .for_each(move |x| tx.send(x).unwrap()); |
| /// |
| /// let v: Vec<_> = rx.iter().collect(); |
| /// assert_eq!(v, vec![1, 3, 5, 7, 9]); |
| /// ``` |
| /// |
| /// For such a small example, a `for` loop may be cleaner, but `for_each` |
| /// might be preferable to keep a functional style with longer iterators: |
| /// |
| /// ``` |
| /// (0..5).flat_map(|x| x * 100 .. x * 110) |
| /// .enumerate() |
| /// .filter(|&(i, x)| (i + x) % 3 == 0) |
| /// .for_each(|(i, x)| println!("{}:{}", i, x)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iterator_for_each", since = "1.21.0")] |
| fn for_each<F>(self, f: F) |
| where |
| Self: Sized, |
| F: FnMut(Self::Item), |
| { |
| #[inline] |
| fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) { |
| move |(), item| f(item) |
| } |
| |
| self.fold((), call(f)); |
| } |
| |
| /// Creates an iterator which uses a closure to determine if an element |
| /// should be yielded. |
| /// |
| /// The closure must return `true` or `false`. `filter()` creates an |
| /// iterator which calls this closure on each element. If the closure |
| /// returns `true`, then the element is returned. If the closure returns |
| /// `false`, it will try again, and call the closure on the next element, |
| /// seeing if it passes the test. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [0i32, 1, 2]; |
| /// |
| /// let mut iter = a.iter().filter(|x| x.is_positive()); |
| /// |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Because the closure passed to `filter()` takes a reference, and many |
| /// iterators iterate over references, this leads to a possibly confusing |
| /// situation, where the type of the closure is a double reference: |
| /// |
| /// ``` |
| /// let a = [0, 1, 2]; |
| /// |
| /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! |
| /// |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// It's common to instead use destructuring on the argument to strip away |
| /// one: |
| /// |
| /// ``` |
| /// let a = [0, 1, 2]; |
| /// |
| /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * |
| /// |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// or both: |
| /// |
| /// ``` |
| /// let a = [0, 1, 2]; |
| /// |
| /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s |
| /// |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// of these layers. |
| /// |
| /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`. |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn filter<P>(self, predicate: P) -> Filter<Self, P> |
| where |
| Self: Sized, |
| P: FnMut(&Self::Item) -> bool, |
| { |
| Filter::new(self, predicate) |
| } |
| |
| /// Creates an iterator that both filters and maps. |
| /// |
| /// The closure must return an [`Option<T>`]. `filter_map` creates an |
| /// iterator which calls this closure on each element. If the closure |
| /// returns [`Some(element)`][`Some`], then that element is returned. If the |
| /// closure returns [`None`], it will try again, and call the closure on the |
| /// next element, seeing if it will return [`Some`]. |
| /// |
| /// Why `filter_map` and not just [`filter`] and [`map`]? The key is in this |
| /// part: |
| /// |
| /// [`filter`]: #method.filter |
| /// [`map`]: #method.map |
| /// |
| /// > If the closure returns [`Some(element)`][`Some`], then that element is returned. |
| /// |
| /// In other words, it removes the [`Option<T>`] layer automatically. If your |
| /// mapping is already returning an [`Option<T>`] and you want to skip over |
| /// [`None`]s, then `filter_map` is much, much nicer to use. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = ["1", "lol", "3", "NaN", "5"]; |
| /// |
| /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); |
| /// |
| /// assert_eq!(iter.next(), Some(1)); |
| /// assert_eq!(iter.next(), Some(3)); |
| /// assert_eq!(iter.next(), Some(5)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Here's the same example, but with [`filter`] and [`map`]: |
| /// |
| /// ``` |
| /// let a = ["1", "lol", "3", "NaN", "5"]; |
| /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); |
| /// assert_eq!(iter.next(), Some(1)); |
| /// assert_eq!(iter.next(), Some(3)); |
| /// assert_eq!(iter.next(), Some(5)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// [`Option<T>`]: ../../std/option/enum.Option.html |
| /// [`Some`]: ../../std/option/enum.Option.html#variant.Some |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> Option<B>, |
| { |
| FilterMap::new(self, f) |
| } |
| |
| /// Creates an iterator which gives the current iteration count as well as |
| /// the next value. |
| /// |
| /// The iterator returned yields pairs `(i, val)`, where `i` is the |
| /// current index of iteration and `val` is the value returned by the |
| /// iterator. |
| /// |
| /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a |
| /// different sized integer, the [`zip`] function provides similar |
| /// functionality. |
| /// |
| /// # Overflow Behavior |
| /// |
| /// The method does no guarding against overflows, so enumerating more than |
| /// [`usize::MAX`] elements either produces the wrong result or panics. If |
| /// debug assertions are enabled, a panic is guaranteed. |
| /// |
| /// # Panics |
| /// |
| /// The returned iterator might panic if the to-be-returned index would |
| /// overflow a [`usize`]. |
| /// |
| /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
| /// [`usize`]: ../../std/primitive.usize.html |
| /// [`zip`]: #method.zip |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = ['a', 'b', 'c']; |
| /// |
| /// let mut iter = a.iter().enumerate(); |
| /// |
| /// assert_eq!(iter.next(), Some((0, &'a'))); |
| /// assert_eq!(iter.next(), Some((1, &'b'))); |
| /// assert_eq!(iter.next(), Some((2, &'c'))); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn enumerate(self) -> Enumerate<Self> |
| where |
| Self: Sized, |
| { |
| Enumerate::new(self) |
| } |
| |
| /// Creates an iterator which can use `peek` to look at the next element of |
| /// the iterator without consuming it. |
| /// |
| /// Adds a [`peek`] method to an iterator. See its documentation for |
| /// more information. |
| /// |
| /// Note that the underlying iterator is still advanced when [`peek`] is |
| /// called for the first time: In order to retrieve the next element, |
| /// [`next`] is called on the underlying iterator, hence any side effects (i.e. |
| /// anything other than fetching the next value) of the [`next`] method |
| /// will occur. |
| /// |
| /// [`peek`]: struct.Peekable.html#method.peek |
| /// [`next`]: ../../std/iter/trait.Iterator.html#tymethod.next |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let xs = [1, 2, 3]; |
| /// |
| /// let mut iter = xs.iter().peekable(); |
| /// |
| /// // peek() lets us see into the future |
| /// assert_eq!(iter.peek(), Some(&&1)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// |
| /// // we can peek() multiple times, the iterator won't advance |
| /// assert_eq!(iter.peek(), Some(&&3)); |
| /// assert_eq!(iter.peek(), Some(&&3)); |
| /// |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// |
| /// // after the iterator is finished, so is peek() |
| /// assert_eq!(iter.peek(), None); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn peekable(self) -> Peekable<Self> |
| where |
| Self: Sized, |
| { |
| Peekable::new(self) |
| } |
| |
| /// Creates an iterator that [`skip`]s elements based on a predicate. |
| /// |
| /// [`skip`]: #method.skip |
| /// |
| /// `skip_while()` takes a closure as an argument. It will call this |
| /// closure on each element of the iterator, and ignore elements |
| /// until it returns `false`. |
| /// |
| /// After `false` is returned, `skip_while()`'s job is over, and the |
| /// rest of the elements are yielded. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [-1i32, 0, 1]; |
| /// |
| /// let mut iter = a.iter().skip_while(|x| x.is_negative()); |
| /// |
| /// assert_eq!(iter.next(), Some(&0)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Because the closure passed to `skip_while()` takes a reference, and many |
| /// iterators iterate over references, this leads to a possibly confusing |
| /// situation, where the type of the closure is a double reference: |
| /// |
| /// ``` |
| /// let a = [-1, 0, 1]; |
| /// |
| /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! |
| /// |
| /// assert_eq!(iter.next(), Some(&0)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Stopping after an initial `false`: |
| /// |
| /// ``` |
| /// let a = [-1, 0, 1, -2]; |
| /// |
| /// let mut iter = a.iter().skip_while(|x| **x < 0); |
| /// |
| /// assert_eq!(iter.next(), Some(&0)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// |
| /// // while this would have been false, since we already got a false, |
| /// // skip_while() isn't used any more |
| /// assert_eq!(iter.next(), Some(&-2)); |
| /// |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> |
| where |
| Self: Sized, |
| P: FnMut(&Self::Item) -> bool, |
| { |
| SkipWhile::new(self, predicate) |
| } |
| |
| /// Creates an iterator that yields elements based on a predicate. |
| /// |
| /// `take_while()` takes a closure as an argument. It will call this |
| /// closure on each element of the iterator, and yield elements |
| /// while it returns `true`. |
| /// |
| /// After `false` is returned, `take_while()`'s job is over, and the |
| /// rest of the elements are ignored. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [-1i32, 0, 1]; |
| /// |
| /// let mut iter = a.iter().take_while(|x| x.is_negative()); |
| /// |
| /// assert_eq!(iter.next(), Some(&-1)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Because the closure passed to `take_while()` takes a reference, and many |
| /// iterators iterate over references, this leads to a possibly confusing |
| /// situation, where the type of the closure is a double reference: |
| /// |
| /// ``` |
| /// let a = [-1, 0, 1]; |
| /// |
| /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! |
| /// |
| /// assert_eq!(iter.next(), Some(&-1)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Stopping after an initial `false`: |
| /// |
| /// ``` |
| /// let a = [-1, 0, 1, -2]; |
| /// |
| /// let mut iter = a.iter().take_while(|x| **x < 0); |
| /// |
| /// assert_eq!(iter.next(), Some(&-1)); |
| /// |
| /// // We have more elements that are less than zero, but since we already |
| /// // got a false, take_while() isn't used any more |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Because `take_while()` needs to look at the value in order to see if it |
| /// should be included or not, consuming iterators will see that it is |
| /// removed: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3, 4]; |
| /// let mut iter = a.iter(); |
| /// |
| /// let result: Vec<i32> = iter.by_ref() |
| /// .take_while(|n| **n != 3) |
| /// .cloned() |
| /// .collect(); |
| /// |
| /// assert_eq!(result, &[1, 2]); |
| /// |
| /// let result: Vec<i32> = iter.cloned().collect(); |
| /// |
| /// assert_eq!(result, &[4]); |
| /// ``` |
| /// |
| /// The `3` is no longer there, because it was consumed in order to see if |
| /// the iteration should stop, but wasn't placed back into the iterator. |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> |
| where |
| Self: Sized, |
| P: FnMut(&Self::Item) -> bool, |
| { |
| TakeWhile::new(self, predicate) |
| } |
| |
| /// Creates an iterator that both yields elements based on a predicate and maps. |
| /// |
| /// `map_while()` takes a closure as an argument. It will call this |
| /// closure on each element of the iterator, and yield elements |
| /// while it returns [`Some(_)`][`Some`]. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(iter_map_while)] |
| /// let a = [-1i32, 4, 0, 1]; |
| /// |
| /// let mut iter = a.iter().map_while(|x| 16i32.checked_div(*x)); |
| /// |
| /// assert_eq!(iter.next(), Some(-16)); |
| /// assert_eq!(iter.next(), Some(4)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Here's the same example, but with [`take_while`] and [`map`]: |
| /// |
| /// [`take_while`]: #method.take_while |
| /// [`map`]: #method.map |
| /// |
| /// ``` |
| /// let a = [-1i32, 4, 0, 1]; |
| /// |
| /// let mut iter = a.iter() |
| /// .map(|x| 16i32.checked_div(*x)) |
| /// .take_while(|x| x.is_some()) |
| /// .map(|x| x.unwrap()); |
| /// |
| /// assert_eq!(iter.next(), Some(-16)); |
| /// assert_eq!(iter.next(), Some(4)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// Stopping after an initial [`None`]: |
| /// |
| /// ``` |
| /// #![feature(iter_map_while)] |
| /// use std::convert::TryFrom; |
| /// |
| /// let a = [0, 1, 2, -3, 4, 5, -6]; |
| /// |
| /// let iter = a.iter().map_while(|x| u32::try_from(*x).ok()); |
| /// let vec = iter.collect::<Vec<_>>(); |
| /// |
| /// // We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3` |
| /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` entcountered. |
| /// assert_eq!(vec, vec![0, 1, 2]); |
| /// ``` |
| /// |
| /// Because `map_while()` needs to look at the value in order to see if it |
| /// should be included or not, consuming iterators will see that it is |
| /// removed: |
| /// |
| /// ``` |
| /// #![feature(iter_map_while)] |
| /// use std::convert::TryFrom; |
| /// |
| /// let a = [1, 2, -3, 4]; |
| /// let mut iter = a.iter(); |
| /// |
| /// let result: Vec<u32> = iter.by_ref() |
| /// .map_while(|n| u32::try_from(*n).ok()) |
| /// .collect(); |
| /// |
| /// assert_eq!(result, &[1, 2]); |
| /// |
| /// let result: Vec<i32> = iter.cloned().collect(); |
| /// |
| /// assert_eq!(result, &[4]); |
| /// ``` |
| /// |
| /// The `-3` is no longer there, because it was consumed in order to see if |
| /// the iteration should stop, but wasn't placed back into the iterator. |
| /// |
| /// Note that unlike [`take_while`] this iterator is **not** fused. |
| /// It is also not specified what this iterator returns after the first` None` is returned. |
| /// If you need fused iterator, use [`fuse`]. |
| /// |
| /// [`Some`]: ../../std/option/enum.Option.html#variant.Some |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`fuse`]: #method.fuse |
| #[inline] |
| #[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")] |
| fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> |
| where |
| Self: Sized, |
| P: FnMut(Self::Item) -> Option<B>, |
| { |
| MapWhile::new(self, predicate) |
| } |
| |
| /// Creates an iterator that skips the first `n` elements. |
| /// |
| /// After they have been consumed, the rest of the elements are yielded. |
| /// Rather than overriding this method directly, instead override the `nth` method. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter().skip(2); |
| /// |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn skip(self, n: usize) -> Skip<Self> |
| where |
| Self: Sized, |
| { |
| Skip::new(self, n) |
| } |
| |
| /// Creates an iterator that yields its first `n` elements. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter().take(2); |
| /// |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// `take()` is often used with an infinite iterator, to make it finite: |
| /// |
| /// ``` |
| /// let mut iter = (0..).take(3); |
| /// |
| /// assert_eq!(iter.next(), Some(0)); |
| /// assert_eq!(iter.next(), Some(1)); |
| /// assert_eq!(iter.next(), Some(2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| /// |
| /// If less than `n` elements are available, |
| /// `take` will limit itself to the size of the underlying iterator: |
| /// |
| /// ``` |
| /// let v = vec![1, 2]; |
| /// let mut iter = v.into_iter().take(5); |
| /// assert_eq!(iter.next(), Some(1)); |
| /// assert_eq!(iter.next(), Some(2)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn take(self, n: usize) -> Take<Self> |
| where |
| Self: Sized, |
| { |
| Take::new(self, n) |
| } |
| |
| /// An iterator adaptor similar to [`fold`] that holds internal state and |
| /// produces a new iterator. |
| /// |
| /// [`fold`]: #method.fold |
| /// |
| /// `scan()` takes two arguments: an initial value which seeds the internal |
| /// state, and a closure with two arguments, the first being a mutable |
| /// reference to the internal state and the second an iterator element. |
| /// The closure can assign to the internal state to share state between |
| /// iterations. |
| /// |
| /// On iteration, the closure will be applied to each element of the |
| /// iterator and the return value from the closure, an [`Option`], is |
| /// yielded by the iterator. |
| /// |
| /// [`Option`]: ../../std/option/enum.Option.html |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter().scan(1, |state, &x| { |
| /// // each iteration, we'll multiply the state by the element |
| /// *state = *state * x; |
| /// |
| /// // then, we'll yield the negation of the state |
| /// Some(-*state) |
| /// }); |
| /// |
| /// assert_eq!(iter.next(), Some(-1)); |
| /// assert_eq!(iter.next(), Some(-2)); |
| /// assert_eq!(iter.next(), Some(-6)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> |
| where |
| Self: Sized, |
| F: FnMut(&mut St, Self::Item) -> Option<B>, |
| { |
| Scan::new(self, initial_state, f) |
| } |
| |
| /// Creates an iterator that works like map, but flattens nested structure. |
| /// |
| /// The [`map`] adapter is very useful, but only when the closure |
| /// argument produces values. If it produces an iterator instead, there's |
| /// an extra layer of indirection. `flat_map()` will remove this extra layer |
| /// on its own. |
| /// |
| /// You can think of `flat_map(f)` as the semantic equivalent |
| /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. |
| /// |
| /// Another way of thinking about `flat_map()`: [`map`]'s closure returns |
| /// one item for each element, and `flat_map()`'s closure returns an |
| /// iterator for each element. |
| /// |
| /// [`map`]: #method.map |
| /// [`flatten`]: #method.flatten |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let words = ["alpha", "beta", "gamma"]; |
| /// |
| /// // chars() returns an iterator |
| /// let merged: String = words.iter() |
| /// .flat_map(|s| s.chars()) |
| /// .collect(); |
| /// assert_eq!(merged, "alphabetagamma"); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> |
| where |
| Self: Sized, |
| U: IntoIterator, |
| F: FnMut(Self::Item) -> U, |
| { |
| FlatMap::new(self, f) |
| } |
| |
| /// Creates an iterator that flattens nested structure. |
| /// |
| /// This is useful when you have an iterator of iterators or an iterator of |
| /// things that can be turned into iterators and you want to remove one |
| /// level of indirection. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; |
| /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>(); |
| /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); |
| /// ``` |
| /// |
| /// Mapping and then flattening: |
| /// |
| /// ``` |
| /// let words = ["alpha", "beta", "gamma"]; |
| /// |
| /// // chars() returns an iterator |
| /// let merged: String = words.iter() |
| /// .map(|s| s.chars()) |
| /// .flatten() |
| /// .collect(); |
| /// assert_eq!(merged, "alphabetagamma"); |
| /// ``` |
| /// |
| /// You can also rewrite this in terms of [`flat_map()`], which is preferable |
| /// in this case since it conveys intent more clearly: |
| /// |
| /// ``` |
| /// let words = ["alpha", "beta", "gamma"]; |
| /// |
| /// // chars() returns an iterator |
| /// let merged: String = words.iter() |
| /// .flat_map(|s| s.chars()) |
| /// .collect(); |
| /// assert_eq!(merged, "alphabetagamma"); |
| /// ``` |
| /// |
| /// Flattening once only removes one level of nesting: |
| /// |
| /// ``` |
| /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; |
| /// |
| /// let d2 = d3.iter().flatten().collect::<Vec<_>>(); |
| /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); |
| /// |
| /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>(); |
| /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); |
| /// ``` |
| /// |
| /// Here we see that `flatten()` does not perform a "deep" flatten. |
| /// Instead, only one level of nesting is removed. That is, if you |
| /// `flatten()` a three-dimensional array the result will be |
| /// two-dimensional and not one-dimensional. To get a one-dimensional |
| /// structure, you have to `flatten()` again. |
| /// |
| /// [`flat_map()`]: #method.flat_map |
| #[inline] |
| #[stable(feature = "iterator_flatten", since = "1.29.0")] |
| fn flatten(self) -> Flatten<Self> |
| where |
| Self: Sized, |
| Self::Item: IntoIterator, |
| { |
| Flatten::new(self) |
| } |
| |
| /// Creates an iterator which ends after the first [`None`]. |
| /// |
| /// After an iterator returns [`None`], future calls may or may not yield |
| /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a |
| /// [`None`] is given, it will always return [`None`] forever. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`Some(T)`]: ../../std/option/enum.Option.html#variant.Some |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// // an iterator which alternates between Some and None |
| /// struct Alternate { |
| /// state: i32, |
| /// } |
| /// |
| /// impl Iterator for Alternate { |
| /// type Item = i32; |
| /// |
| /// fn next(&mut self) -> Option<i32> { |
| /// let val = self.state; |
| /// self.state = self.state + 1; |
| /// |
| /// // if it's even, Some(i32), else None |
| /// if val % 2 == 0 { |
| /// Some(val) |
| /// } else { |
| /// None |
| /// } |
| /// } |
| /// } |
| /// |
| /// let mut iter = Alternate { state: 0 }; |
| /// |
| /// // we can see our iterator going back and forth |
| /// assert_eq!(iter.next(), Some(0)); |
| /// assert_eq!(iter.next(), None); |
| /// assert_eq!(iter.next(), Some(2)); |
| /// assert_eq!(iter.next(), None); |
| /// |
| /// // however, once we fuse it... |
| /// let mut iter = iter.fuse(); |
| /// |
| /// assert_eq!(iter.next(), Some(4)); |
| /// assert_eq!(iter.next(), None); |
| /// |
| /// // it will always return `None` after the first time. |
| /// assert_eq!(iter.next(), None); |
| /// assert_eq!(iter.next(), None); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn fuse(self) -> Fuse<Self> |
| where |
| Self: Sized, |
| { |
| Fuse::new(self) |
| } |
| |
| /// Does something with each element of an iterator, passing the value on. |
| /// |
| /// When using iterators, you'll often chain several of them together. |
| /// While working on such code, you might want to check out what's |
| /// happening at various parts in the pipeline. To do that, insert |
| /// a call to `inspect()`. |
| /// |
| /// It's more common for `inspect()` to be used as a debugging tool than to |
| /// exist in your final code, but applications may find it useful in certain |
| /// situations when errors need to be logged before being discarded. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 4, 2, 3]; |
| /// |
| /// // this iterator sequence is complex. |
| /// let sum = a.iter() |
| /// .cloned() |
| /// .filter(|x| x % 2 == 0) |
| /// .fold(0, |sum, i| sum + i); |
| /// |
| /// println!("{}", sum); |
| /// |
| /// // let's add some inspect() calls to investigate what's happening |
| /// let sum = a.iter() |
| /// .cloned() |
| /// .inspect(|x| println!("about to filter: {}", x)) |
| /// .filter(|x| x % 2 == 0) |
| /// .inspect(|x| println!("made it through filter: {}", x)) |
| /// .fold(0, |sum, i| sum + i); |
| /// |
| /// println!("{}", sum); |
| /// ``` |
| /// |
| /// This will print: |
| /// |
| /// ```text |
| /// 6 |
| /// about to filter: 1 |
| /// about to filter: 4 |
| /// made it through filter: 4 |
| /// about to filter: 2 |
| /// made it through filter: 2 |
| /// about to filter: 3 |
| /// 6 |
| /// ``` |
| /// |
| /// Logging errors before discarding them: |
| /// |
| /// ``` |
| /// let lines = ["1", "2", "a"]; |
| /// |
| /// let sum: i32 = lines |
| /// .iter() |
| /// .map(|line| line.parse::<i32>()) |
| /// .inspect(|num| { |
| /// if let Err(ref e) = *num { |
| /// println!("Parsing error: {}", e); |
| /// } |
| /// }) |
| /// .filter_map(Result::ok) |
| /// .sum(); |
| /// |
| /// println!("Sum: {}", sum); |
| /// ``` |
| /// |
| /// This will print: |
| /// |
| /// ```text |
| /// Parsing error: invalid digit found in string |
| /// Sum: 3 |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn inspect<F>(self, f: F) -> Inspect<Self, F> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item), |
| { |
| Inspect::new(self, f) |
| } |
| |
| /// Borrows an iterator, rather than consuming it. |
| /// |
| /// This is useful to allow applying iterator adaptors while still |
| /// retaining ownership of the original iterator. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let iter = a.iter(); |
| /// |
| /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i ); |
| /// |
| /// assert_eq!(sum, 6); |
| /// |
| /// // if we try to use iter again, it won't work. The following line |
| /// // gives "error: use of moved value: `iter` |
| /// // assert_eq!(iter.next(), None); |
| /// |
| /// // let's try that again |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// // instead, we add in a .by_ref() |
| /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i ); |
| /// |
| /// assert_eq!(sum, 3); |
| /// |
| /// // now this is just fine: |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn by_ref(&mut self) -> &mut Self |
| where |
| Self: Sized, |
| { |
| self |
| } |
| |
| /// Transforms an iterator into a collection. |
| /// |
| /// `collect()` can take anything iterable, and turn it into a relevant |
| /// collection. This is one of the more powerful methods in the standard |
| /// library, used in a variety of contexts. |
| /// |
| /// The most basic pattern in which `collect()` is used is to turn one |
| /// collection into another. You take a collection, call [`iter`] on it, |
| /// do a bunch of transformations, and then `collect()` at the end. |
| /// |
| /// One of the keys to `collect()`'s power is that many things you might |
| /// not think of as 'collections' actually are. For example, a [`String`] |
| /// is a collection of [`char`]s. And a collection of |
| /// [`Result<T, E>`][`Result`] can be thought of as single |
| /// [`Result`]`<Collection<T>, E>`. See the examples below for more. |
| /// |
| /// Because `collect()` is so general, it can cause problems with type |
| /// inference. As such, `collect()` is one of the few times you'll see |
| /// the syntax affectionately known as the 'turbofish': `::<>`. This |
| /// helps the inference algorithm understand specifically which collection |
| /// you're trying to collect into. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let doubled: Vec<i32> = a.iter() |
| /// .map(|&x| x * 2) |
| /// .collect(); |
| /// |
| /// assert_eq!(vec![2, 4, 6], doubled); |
| /// ``` |
| /// |
| /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because |
| /// we could collect into, for example, a [`VecDeque<T>`] instead: |
| /// |
| /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html |
| /// |
| /// ``` |
| /// use std::collections::VecDeque; |
| /// |
| /// let a = [1, 2, 3]; |
| /// |
| /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect(); |
| /// |
| /// assert_eq!(2, doubled[0]); |
| /// assert_eq!(4, doubled[1]); |
| /// assert_eq!(6, doubled[2]); |
| /// ``` |
| /// |
| /// Using the 'turbofish' instead of annotating `doubled`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>(); |
| /// |
| /// assert_eq!(vec![2, 4, 6], doubled); |
| /// ``` |
| /// |
| /// Because `collect()` only cares about what you're collecting into, you can |
| /// still use a partial type hint, `_`, with the turbofish: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>(); |
| /// |
| /// assert_eq!(vec![2, 4, 6], doubled); |
| /// ``` |
| /// |
| /// Using `collect()` to make a [`String`]: |
| /// |
| /// ``` |
| /// let chars = ['g', 'd', 'k', 'k', 'n']; |
| /// |
| /// let hello: String = chars.iter() |
| /// .map(|&x| x as u8) |
| /// .map(|x| (x + 1) as char) |
| /// .collect(); |
| /// |
| /// assert_eq!("hello", hello); |
| /// ``` |
| /// |
| /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to |
| /// see if any of them failed: |
| /// |
| /// ``` |
| /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; |
| /// |
| /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); |
| /// |
| /// // gives us the first error |
| /// assert_eq!(Err("nope"), result); |
| /// |
| /// let results = [Ok(1), Ok(3)]; |
| /// |
| /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect(); |
| /// |
| /// // gives us the list of answers |
| /// assert_eq!(Ok(vec![1, 3]), result); |
| /// ``` |
| /// |
| /// [`iter`]: ../../std/iter/trait.Iterator.html#tymethod.next |
| /// [`String`]: ../../std/string/struct.String.html |
| /// [`char`]: ../../std/primitive.char.html |
| /// [`Result`]: ../../std/result/enum.Result.html |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] |
| fn collect<B: FromIterator<Self::Item>>(self) -> B |
| where |
| Self: Sized, |
| { |
| FromIterator::from_iter(self) |
| } |
| |
| /// Consumes an iterator, creating two collections from it. |
| /// |
| /// The predicate passed to `partition()` can return `true`, or `false`. |
| /// `partition()` returns a pair, all of the elements for which it returned |
| /// `true`, and all of the elements for which it returned `false`. |
| /// |
| /// See also [`is_partitioned()`] and [`partition_in_place()`]. |
| /// |
| /// [`is_partitioned()`]: #method.is_partitioned |
| /// [`partition_in_place()`]: #method.partition_in_place |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let (even, odd): (Vec<i32>, Vec<i32>) = a |
| /// .iter() |
| /// .partition(|&n| n % 2 == 0); |
| /// |
| /// assert_eq!(even, vec![2]); |
| /// assert_eq!(odd, vec![1, 3]); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn partition<B, F>(self, f: F) -> (B, B) |
| where |
| Self: Sized, |
| B: Default + Extend<Self::Item>, |
| F: FnMut(&Self::Item) -> bool, |
| { |
| #[inline] |
| fn extend<'a, T, B: Extend<T>>( |
| mut f: impl FnMut(&T) -> bool + 'a, |
| left: &'a mut B, |
| right: &'a mut B, |
| ) -> impl FnMut((), T) + 'a { |
| move |(), x| { |
| if f(&x) { |
| left.extend_one(x); |
| } else { |
| right.extend_one(x); |
| } |
| } |
| } |
| |
| let mut left: B = Default::default(); |
| let mut right: B = Default::default(); |
| |
| self.fold((), extend(f, &mut left, &mut right)); |
| |
| (left, right) |
| } |
| |
| /// Reorders the elements of this iterator *in-place* according to the given predicate, |
| /// such that all those that return `true` precede all those that return `false`. |
| /// Returns the number of `true` elements found. |
| /// |
| /// The relative order of partitioned items is not maintained. |
| /// |
| /// See also [`is_partitioned()`] and [`partition()`]. |
| /// |
| /// [`is_partitioned()`]: #method.is_partitioned |
| /// [`partition()`]: #method.partition |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(iter_partition_in_place)] |
| /// |
| /// let mut a = [1, 2, 3, 4, 5, 6, 7]; |
| /// |
| /// // Partition in-place between evens and odds |
| /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0); |
| /// |
| /// assert_eq!(i, 3); |
| /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens |
| /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds |
| /// ``` |
| #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")] |
| fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize |
| where |
| Self: Sized + DoubleEndedIterator<Item = &'a mut T>, |
| P: FnMut(&T) -> bool, |
| { |
| // FIXME: should we worry about the count overflowing? The only way to have more than |
| // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition... |
| |
| // These closure "factory" functions exist to avoid genericity in `Self`. |
| |
| #[inline] |
| fn is_false<'a, T>( |
| predicate: &'a mut impl FnMut(&T) -> bool, |
| true_count: &'a mut usize, |
| ) -> impl FnMut(&&mut T) -> bool + 'a { |
| move |x| { |
| let p = predicate(&**x); |
| *true_count += p as usize; |
| !p |
| } |
| } |
| |
| #[inline] |
| fn is_true<T>(predicate: &mut impl FnMut(&T) -> bool) -> impl FnMut(&&mut T) -> bool + '_ { |
| move |x| predicate(&**x) |
| } |
| |
| // Repeatedly find the first `false` and swap it with the last `true`. |
| let mut true_count = 0; |
| while let Some(head) = self.find(is_false(predicate, &mut true_count)) { |
| if let Some(tail) = self.rfind(is_true(predicate)) { |
| crate::mem::swap(head, tail); |
| true_count += 1; |
| } else { |
| break; |
| } |
| } |
| true_count |
| } |
| |
| /// Checks if the elements of this iterator are partitioned according to the given predicate, |
| /// such that all those that return `true` precede all those that return `false`. |
| /// |
| /// See also [`partition()`] and [`partition_in_place()`]. |
| /// |
| /// [`partition()`]: #method.partition |
| /// [`partition_in_place()`]: #method.partition_in_place |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(iter_is_partitioned)] |
| /// |
| /// assert!("Iterator".chars().is_partitioned(char::is_uppercase)); |
| /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase)); |
| /// ``` |
| #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")] |
| fn is_partitioned<P>(mut self, mut predicate: P) -> bool |
| where |
| Self: Sized, |
| P: FnMut(Self::Item) -> bool, |
| { |
| // Either all items test `true`, or the first clause stops at `false` |
| // and we check that there are no more `true` items after that. |
| self.all(&mut predicate) || !self.any(predicate) |
| } |
| |
| /// An iterator method that applies a function as long as it returns |
| /// successfully, producing a single, final value. |
| /// |
| /// `try_fold()` takes two arguments: an initial value, and a closure with |
| /// two arguments: an 'accumulator', and an element. The closure either |
| /// returns successfully, with the value that the accumulator should have |
| /// for the next iteration, or it returns failure, with an error value that |
| /// is propagated back to the caller immediately (short-circuiting). |
| /// |
| /// The initial value is the value the accumulator will have on the first |
| /// call. If applying the closure succeeded against every element of the |
| /// iterator, `try_fold()` returns the final accumulator as success. |
| /// |
| /// Folding is useful whenever you have a collection of something, and want |
| /// to produce a single value from it. |
| /// |
| /// # Note to Implementors |
| /// |
| /// Several of the other (forward) methods have default implementations in |
| /// terms of this one, so try to implement this explicitly if it can |
| /// do something better than the default `for` loop implementation. |
| /// |
| /// In particular, try to have this call `try_fold()` on the internal parts |
| /// from which this iterator is composed. If multiple calls are needed, |
| /// the `?` operator may be convenient for chaining the accumulator value |
| /// along, but beware any invariants that need to be upheld before those |
| /// early returns. This is a `&mut self` method, so iteration needs to be |
| /// resumable after hitting an error here. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// // the checked sum of all of the elements of the array |
| /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); |
| /// |
| /// assert_eq!(sum, Some(6)); |
| /// ``` |
| /// |
| /// Short-circuiting: |
| /// |
| /// ``` |
| /// let a = [10, 20, 30, 100, 40, 50]; |
| /// let mut it = a.iter(); |
| /// |
| /// // This sum overflows when adding the 100 element |
| /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); |
| /// assert_eq!(sum, None); |
| /// |
| /// // Because it short-circuited, the remaining elements are still |
| /// // available through the iterator. |
| /// assert_eq!(it.len(), 2); |
| /// assert_eq!(it.next(), Some(&40)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
| fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R |
| where |
| Self: Sized, |
| F: FnMut(B, Self::Item) -> R, |
| R: Try<Ok = B>, |
| { |
| let mut accum = init; |
| while let Some(x) = self.next() { |
| accum = f(accum, x)?; |
| } |
| Try::from_ok(accum) |
| } |
| |
| /// An iterator method that applies a fallible function to each item in the |
| /// iterator, stopping at the first error and returning that error. |
| /// |
| /// This can also be thought of as the fallible form of [`for_each()`] |
| /// or as the stateless version of [`try_fold()`]. |
| /// |
| /// [`for_each()`]: #method.for_each |
| /// [`try_fold()`]: #method.try_fold |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::fs::rename; |
| /// use std::io::{stdout, Write}; |
| /// use std::path::Path; |
| /// |
| /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; |
| /// |
| /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{}", x)); |
| /// assert!(res.is_ok()); |
| /// |
| /// let mut it = data.iter().cloned(); |
| /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); |
| /// assert!(res.is_err()); |
| /// // It short-circuited, so the remaining items are still in the iterator: |
| /// assert_eq!(it.next(), Some("stale_bread.json")); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iterator_try_fold", since = "1.27.0")] |
| fn try_for_each<F, R>(&mut self, f: F) -> R |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> R, |
| R: Try<Ok = ()>, |
| { |
| #[inline] |
| fn call<T, R>(mut f: impl FnMut(T) -> R) -> impl FnMut((), T) -> R { |
| move |(), x| f(x) |
| } |
| |
| self.try_fold((), call(f)) |
| } |
| |
| /// An iterator method that applies a function, producing a single, final value. |
| /// |
| /// `fold()` takes two arguments: an initial value, and a closure with two |
| /// arguments: an 'accumulator', and an element. The closure returns the value that |
| /// the accumulator should have for the next iteration. |
| /// |
| /// The initial value is the value the accumulator will have on the first |
| /// call. |
| /// |
| /// After applying this closure to every element of the iterator, `fold()` |
| /// returns the accumulator. |
| /// |
| /// This operation is sometimes called 'reduce' or 'inject'. |
| /// |
| /// Folding is useful whenever you have a collection of something, and want |
| /// to produce a single value from it. |
| /// |
| /// Note: `fold()`, and similar methods that traverse the entire iterator, |
| /// may not terminate for infinite iterators, even on traits for which a |
| /// result is determinable in finite time. |
| /// |
| /// # Note to Implementors |
| /// |
| /// Several of the other (forward) methods have default implementations in |
| /// terms of this one, so try to implement this explicitly if it can |
| /// do something better than the default `for` loop implementation. |
| /// |
| /// In particular, try to have this call `fold()` on the internal parts |
| /// from which this iterator is composed. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// // the sum of all of the elements of the array |
| /// let sum = a.iter().fold(0, |acc, x| acc + x); |
| /// |
| /// assert_eq!(sum, 6); |
| /// ``` |
| /// |
| /// Let's walk through each step of the iteration here: |
| /// |
| /// | element | acc | x | result | |
| /// |---------|-----|---|--------| |
| /// | | 0 | | | |
| /// | 1 | 0 | 1 | 1 | |
| /// | 2 | 1 | 2 | 3 | |
| /// | 3 | 3 | 3 | 6 | |
| /// |
| /// And so, our final result, `6`. |
| /// |
| /// It's common for people who haven't used iterators a lot to |
| /// use a `for` loop with a list of things to build up a result. Those |
| /// can be turned into `fold()`s: |
| /// |
| /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for |
| /// |
| /// ``` |
| /// let numbers = [1, 2, 3, 4, 5]; |
| /// |
| /// let mut result = 0; |
| /// |
| /// // for loop: |
| /// for i in &numbers { |
| /// result = result + i; |
| /// } |
| /// |
| /// // fold: |
| /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); |
| /// |
| /// // they're the same |
| /// assert_eq!(result, result2); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn fold<B, F>(mut self, init: B, mut f: F) -> B |
| where |
| Self: Sized, |
| F: FnMut(B, Self::Item) -> B, |
| { |
| let mut accum = init; |
| while let Some(x) = self.next() { |
| accum = f(accum, x); |
| } |
| accum |
| } |
| |
| /// The same as [`fold()`](#method.fold), but uses the first element in the |
| /// iterator as the initial value, folding every subsequent element into it. |
| /// If the iterator is empty, return `None`; otherwise, return the result |
| /// of the fold. |
| /// |
| /// # Example |
| /// |
| /// Find the maximum value: |
| /// |
| /// ``` |
| /// #![feature(iterator_fold_self)] |
| /// |
| /// fn find_max<I>(iter: I) -> Option<I::Item> |
| /// where I: Iterator, |
| /// I::Item: Ord, |
| /// { |
| /// iter.fold_first(|a, b| { |
| /// if a >= b { a } else { b } |
| /// }) |
| /// } |
| /// let a = [10, 20, 5, -23, 0]; |
| /// let b: [u32; 0] = []; |
| /// |
| /// assert_eq!(find_max(a.iter()), Some(&20)); |
| /// assert_eq!(find_max(b.iter()), None); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "iterator_fold_self", issue = "68125")] |
| fn fold_first<F>(mut self, f: F) -> Option<Self::Item> |
| where |
| Self: Sized, |
| F: FnMut(Self::Item, Self::Item) -> Self::Item, |
| { |
| let first = self.next()?; |
| Some(self.fold(first, f)) |
| } |
| |
| /// Tests if every element of the iterator matches a predicate. |
| /// |
| /// `all()` takes a closure that returns `true` or `false`. It applies |
| /// this closure to each element of the iterator, and if they all return |
| /// `true`, then so does `all()`. If any of them return `false`, it |
| /// returns `false`. |
| /// |
| /// `all()` is short-circuiting; in other words, it will stop processing |
| /// as soon as it finds a `false`, given that no matter what else happens, |
| /// the result will also be `false`. |
| /// |
| /// An empty iterator returns `true`. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// assert!(a.iter().all(|&x| x > 0)); |
| /// |
| /// assert!(!a.iter().all(|&x| x > 2)); |
| /// ``` |
| /// |
| /// Stopping at the first `false`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert!(!iter.all(|&x| x != 2)); |
| /// |
| /// // we can still use `iter`, as there are more elements. |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn all<F>(&mut self, f: F) -> bool |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> bool, |
| { |
| #[inline] |
| fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> LoopState<(), ()> { |
| move |(), x| { |
| if f(x) { LoopState::Continue(()) } else { LoopState::Break(()) } |
| } |
| } |
| self.try_fold((), check(f)) == LoopState::Continue(()) |
| } |
| |
| /// Tests if any element of the iterator matches a predicate. |
| /// |
| /// `any()` takes a closure that returns `true` or `false`. It applies |
| /// this closure to each element of the iterator, and if any of them return |
| /// `true`, then so does `any()`. If they all return `false`, it |
| /// returns `false`. |
| /// |
| /// `any()` is short-circuiting; in other words, it will stop processing |
| /// as soon as it finds a `true`, given that no matter what else happens, |
| /// the result will also be `true`. |
| /// |
| /// An empty iterator returns `false`. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// assert!(a.iter().any(|&x| x > 0)); |
| /// |
| /// assert!(!a.iter().any(|&x| x > 5)); |
| /// ``` |
| /// |
| /// Stopping at the first `true`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert!(iter.any(|&x| x != 2)); |
| /// |
| /// // we can still use `iter`, as there are more elements. |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn any<F>(&mut self, f: F) -> bool |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> bool, |
| { |
| #[inline] |
| fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> LoopState<(), ()> { |
| move |(), x| { |
| if f(x) { LoopState::Break(()) } else { LoopState::Continue(()) } |
| } |
| } |
| |
| self.try_fold((), check(f)) == LoopState::Break(()) |
| } |
| |
| /// Searches for an element of an iterator that satisfies a predicate. |
| /// |
| /// `find()` takes a closure that returns `true` or `false`. It applies |
| /// this closure to each element of the iterator, and if any of them return |
| /// `true`, then `find()` returns [`Some(element)`]. If they all return |
| /// `false`, it returns [`None`]. |
| /// |
| /// `find()` is short-circuiting; in other words, it will stop processing |
| /// as soon as the closure returns `true`. |
| /// |
| /// Because `find()` takes a reference, and many iterators iterate over |
| /// references, this leads to a possibly confusing situation where the |
| /// argument is a double reference. You can see this effect in the |
| /// examples below, with `&&x`. |
| /// |
| /// [`Some(element)`]: ../../std/option/enum.Option.html#variant.Some |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); |
| /// |
| /// assert_eq!(a.iter().find(|&&x| x == 5), None); |
| /// ``` |
| /// |
| /// Stopping at the first `true`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); |
| /// |
| /// // we can still use `iter`, as there are more elements. |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// ``` |
| /// |
| /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`. |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn find<P>(&mut self, predicate: P) -> Option<Self::Item> |
| where |
| Self: Sized, |
| P: FnMut(&Self::Item) -> bool, |
| { |
| #[inline] |
| fn check<T>( |
| mut predicate: impl FnMut(&T) -> bool, |
| ) -> impl FnMut((), T) -> LoopState<(), T> { |
| move |(), x| { |
| if predicate(&x) { LoopState::Break(x) } else { LoopState::Continue(()) } |
| } |
| } |
| |
| self.try_fold((), check(predicate)).break_value() |
| } |
| |
| /// Applies function to the elements of iterator and returns |
| /// the first non-none result. |
| /// |
| /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. |
| /// |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = ["lol", "NaN", "2", "5"]; |
| /// |
| /// let first_number = a.iter().find_map(|s| s.parse().ok()); |
| /// |
| /// assert_eq!(first_number, Some(2)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iterator_find_map", since = "1.30.0")] |
| fn find_map<B, F>(&mut self, f: F) -> Option<B> |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> Option<B>, |
| { |
| #[inline] |
| fn check<T, B>(mut f: impl FnMut(T) -> Option<B>) -> impl FnMut((), T) -> LoopState<(), B> { |
| move |(), x| match f(x) { |
| Some(x) => LoopState::Break(x), |
| None => LoopState::Continue(()), |
| } |
| } |
| |
| self.try_fold((), check(f)).break_value() |
| } |
| |
| /// Applies function to the elements of iterator and returns |
| /// the first true result or the first error. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(try_find)] |
| /// |
| /// let a = ["1", "2", "lol", "NaN", "5"]; |
| /// |
| /// let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> { |
| /// Ok(s.parse::<i32>()? == search) |
| /// }; |
| /// |
| /// let result = a.iter().try_find(|&&s| is_my_num(s, 2)); |
| /// assert_eq!(result, Ok(Some(&"2"))); |
| /// |
| /// let result = a.iter().try_find(|&&s| is_my_num(s, 5)); |
| /// assert!(result.is_err()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "try_find", reason = "new API", issue = "63178")] |
| fn try_find<F, R>(&mut self, f: F) -> Result<Option<Self::Item>, R::Error> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item) -> R, |
| R: Try<Ok = bool>, |
| { |
| #[inline] |
| fn check<F, T, R>(mut f: F) -> impl FnMut((), T) -> LoopState<(), Result<T, R::Error>> |
| where |
| F: FnMut(&T) -> R, |
| R: Try<Ok = bool>, |
| { |
| move |(), x| match f(&x).into_result() { |
| Ok(false) => LoopState::Continue(()), |
| Ok(true) => LoopState::Break(Ok(x)), |
| Err(x) => LoopState::Break(Err(x)), |
| } |
| } |
| |
| self.try_fold((), check(f)).break_value().transpose() |
| } |
| |
| /// Searches for an element in an iterator, returning its index. |
| /// |
| /// `position()` takes a closure that returns `true` or `false`. It applies |
| /// this closure to each element of the iterator, and if one of them |
| /// returns `true`, then `position()` returns [`Some(index)`]. If all of |
| /// them return `false`, it returns [`None`]. |
| /// |
| /// `position()` is short-circuiting; in other words, it will stop |
| /// processing as soon as it finds a `true`. |
| /// |
| /// # Overflow Behavior |
| /// |
| /// The method does no guarding against overflows, so if there are more |
| /// than [`usize::MAX`] non-matching elements, it either produces the wrong |
| /// result or panics. If debug assertions are enabled, a panic is |
| /// guaranteed. |
| /// |
| /// # Panics |
| /// |
| /// This function might panic if the iterator has more than `usize::MAX` |
| /// non-matching elements. |
| /// |
| /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); |
| /// |
| /// assert_eq!(a.iter().position(|&x| x == 5), None); |
| /// ``` |
| /// |
| /// Stopping at the first `true`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3, 4]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); |
| /// |
| /// // we can still use `iter`, as there are more elements. |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// |
| /// // The returned index depends on iterator state |
| /// assert_eq!(iter.position(|&x| x == 4), Some(0)); |
| /// |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn position<P>(&mut self, predicate: P) -> Option<usize> |
| where |
| Self: Sized, |
| P: FnMut(Self::Item) -> bool, |
| { |
| #[inline] |
| fn check<T>( |
| mut predicate: impl FnMut(T) -> bool, |
| ) -> impl FnMut(usize, T) -> LoopState<usize, usize> { |
| // The addition might panic on overflow |
| move |i, x| { |
| if predicate(x) { LoopState::Break(i) } else { LoopState::Continue(Add::add(i, 1)) } |
| } |
| } |
| |
| self.try_fold(0, check(predicate)).break_value() |
| } |
| |
| /// Searches for an element in an iterator from the right, returning its |
| /// index. |
| /// |
| /// `rposition()` takes a closure that returns `true` or `false`. It applies |
| /// this closure to each element of the iterator, starting from the end, |
| /// and if one of them returns `true`, then `rposition()` returns |
| /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. |
| /// |
| /// `rposition()` is short-circuiting; in other words, it will stop |
| /// processing as soon as it finds a `true`. |
| /// |
| /// [`Some(index)`]: ../../std/option/enum.Option.html#variant.Some |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); |
| /// |
| /// assert_eq!(a.iter().rposition(|&x| x == 5), None); |
| /// ``` |
| /// |
| /// Stopping at the first `true`: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter(); |
| /// |
| /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); |
| /// |
| /// // we can still use `iter`, as there are more elements. |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn rposition<P>(&mut self, predicate: P) -> Option<usize> |
| where |
| P: FnMut(Self::Item) -> bool, |
| Self: Sized + ExactSizeIterator + DoubleEndedIterator, |
| { |
| // No need for an overflow check here, because `ExactSizeIterator` |
| // implies that the number of elements fits into a `usize`. |
| #[inline] |
| fn check<T>( |
| mut predicate: impl FnMut(T) -> bool, |
| ) -> impl FnMut(usize, T) -> LoopState<usize, usize> { |
| move |i, x| { |
| let i = i - 1; |
| if predicate(x) { LoopState::Break(i) } else { LoopState::Continue(i) } |
| } |
| } |
| |
| let n = self.len(); |
| self.try_rfold(n, check(predicate)).break_value() |
| } |
| |
| /// Returns the maximum element of an iterator. |
| /// |
| /// If several elements are equally maximum, the last element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// let b: Vec<u32> = Vec::new(); |
| /// |
| /// assert_eq!(a.iter().max(), Some(&3)); |
| /// assert_eq!(b.iter().max(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn max(self) -> Option<Self::Item> |
| where |
| Self: Sized, |
| Self::Item: Ord, |
| { |
| self.max_by(Ord::cmp) |
| } |
| |
| /// Returns the minimum element of an iterator. |
| /// |
| /// If several elements are equally minimum, the first element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// let b: Vec<u32> = Vec::new(); |
| /// |
| /// assert_eq!(a.iter().min(), Some(&1)); |
| /// assert_eq!(b.iter().min(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn min(self) -> Option<Self::Item> |
| where |
| Self: Sized, |
| Self::Item: Ord, |
| { |
| self.min_by(Ord::cmp) |
| } |
| |
| /// Returns the element that gives the maximum value from the |
| /// specified function. |
| /// |
| /// If several elements are equally maximum, the last element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [-3_i32, 0, 1, 5, -10]; |
| /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] |
| fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item) -> B, |
| { |
| #[inline] |
| fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { |
| move |x| (f(&x), x) |
| } |
| |
| #[inline] |
| fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { |
| x_p.cmp(y_p) |
| } |
| |
| let (_, x) = self.map(key(f)).max_by(compare)?; |
| Some(x) |
| } |
| |
| /// Returns the element that gives the maximum value with respect to the |
| /// specified comparison function. |
| /// |
| /// If several elements are equally maximum, the last element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [-3_i32, 0, 1, 5, -10]; |
| /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iter_max_by", since = "1.15.0")] |
| fn max_by<F>(self, compare: F) -> Option<Self::Item> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item, &Self::Item) -> Ordering, |
| { |
| #[inline] |
| fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { |
| move |x, y| cmp::max_by(x, y, &mut compare) |
| } |
| |
| self.fold_first(fold(compare)) |
| } |
| |
| /// Returns the element that gives the minimum value from the |
| /// specified function. |
| /// |
| /// If several elements are equally minimum, the first element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [-3_i32, 0, 1, 5, -10]; |
| /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] |
| fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item) -> B, |
| { |
| #[inline] |
| fn key<T, B>(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { |
| move |x| (f(&x), x) |
| } |
| |
| #[inline] |
| fn compare<T, B: Ord>((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { |
| x_p.cmp(y_p) |
| } |
| |
| let (_, x) = self.map(key(f)).min_by(compare)?; |
| Some(x) |
| } |
| |
| /// Returns the element that gives the minimum value with respect to the |
| /// specified comparison function. |
| /// |
| /// If several elements are equally minimum, the first element is |
| /// returned. If the iterator is empty, [`None`] is returned. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [-3_i32, 0, 1, 5, -10]; |
| /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); |
| /// ``` |
| #[inline] |
| #[stable(feature = "iter_min_by", since = "1.15.0")] |
| fn min_by<F>(self, compare: F) -> Option<Self::Item> |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item, &Self::Item) -> Ordering, |
| { |
| #[inline] |
| fn fold<T>(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { |
| move |x, y| cmp::min_by(x, y, &mut compare) |
| } |
| |
| self.fold_first(fold(compare)) |
| } |
| |
| /// Reverses an iterator's direction. |
| /// |
| /// Usually, iterators iterate from left to right. After using `rev()`, |
| /// an iterator will instead iterate from right to left. |
| /// |
| /// This is only possible if the iterator has an end, so `rev()` only |
| /// works on [`DoubleEndedIterator`]s. |
| /// |
| /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut iter = a.iter().rev(); |
| /// |
| /// assert_eq!(iter.next(), Some(&3)); |
| /// assert_eq!(iter.next(), Some(&2)); |
| /// assert_eq!(iter.next(), Some(&1)); |
| /// |
| /// assert_eq!(iter.next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn rev(self) -> Rev<Self> |
| where |
| Self: Sized + DoubleEndedIterator, |
| { |
| Rev::new(self) |
| } |
| |
| /// Converts an iterator of pairs into a pair of containers. |
| /// |
| /// `unzip()` consumes an entire iterator of pairs, producing two |
| /// collections: one from the left elements of the pairs, and one |
| /// from the right elements. |
| /// |
| /// This function is, in some sense, the opposite of [`zip`]. |
| /// |
| /// [`zip`]: #method.zip |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [(1, 2), (3, 4)]; |
| /// |
| /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); |
| /// |
| /// assert_eq!(left, [1, 3]); |
| /// assert_eq!(right, [2, 4]); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) |
| where |
| FromA: Default + Extend<A>, |
| FromB: Default + Extend<B>, |
| Self: Sized + Iterator<Item = (A, B)>, |
| { |
| fn extend<'a, A, B>( |
| ts: &'a mut impl Extend<A>, |
| us: &'a mut impl Extend<B>, |
| ) -> impl FnMut((), (A, B)) + 'a { |
| move |(), (t, u)| { |
| ts.extend_one(t); |
| us.extend_one(u); |
| } |
| } |
| |
| let mut ts: FromA = Default::default(); |
| let mut us: FromB = Default::default(); |
| |
| let (lower_bound, _) = self.size_hint(); |
| if lower_bound > 0 { |
| ts.extend_reserve(lower_bound); |
| us.extend_reserve(lower_bound); |
| } |
| |
| self.fold((), extend(&mut ts, &mut us)); |
| |
| (ts, us) |
| } |
| |
| /// Creates an iterator which copies all of its elements. |
| /// |
| /// This is useful when you have an iterator over `&T`, but you need an |
| /// iterator over `T`. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let v_copied: Vec<_> = a.iter().copied().collect(); |
| /// |
| /// // copied is the same as .map(|&x| x) |
| /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); |
| /// |
| /// assert_eq!(v_copied, vec![1, 2, 3]); |
| /// assert_eq!(v_map, vec![1, 2, 3]); |
| /// ``` |
| #[stable(feature = "iter_copied", since = "1.36.0")] |
| fn copied<'a, T: 'a>(self) -> Copied<Self> |
| where |
| Self: Sized + Iterator<Item = &'a T>, |
| T: Copy, |
| { |
| Copied::new(self) |
| } |
| |
| /// Creates an iterator which [`clone`]s all of its elements. |
| /// |
| /// This is useful when you have an iterator over `&T`, but you need an |
| /// iterator over `T`. |
| /// |
| /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let v_cloned: Vec<_> = a.iter().cloned().collect(); |
| /// |
| /// // cloned is the same as .map(|&x| x), for integers |
| /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); |
| /// |
| /// assert_eq!(v_cloned, vec![1, 2, 3]); |
| /// assert_eq!(v_map, vec![1, 2, 3]); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| fn cloned<'a, T: 'a>(self) -> Cloned<Self> |
| where |
| Self: Sized + Iterator<Item = &'a T>, |
| T: Clone, |
| { |
| Cloned::new(self) |
| } |
| |
| /// Repeats an iterator endlessly. |
| /// |
| /// Instead of stopping at [`None`], the iterator will instead start again, |
| /// from the beginning. After iterating again, it will start at the |
| /// beginning again. And again. And again. Forever. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// |
| /// let mut it = a.iter().cycle(); |
| /// |
| /// assert_eq!(it.next(), Some(&1)); |
| /// assert_eq!(it.next(), Some(&2)); |
| /// assert_eq!(it.next(), Some(&3)); |
| /// assert_eq!(it.next(), Some(&1)); |
| /// assert_eq!(it.next(), Some(&2)); |
| /// assert_eq!(it.next(), Some(&3)); |
| /// assert_eq!(it.next(), Some(&1)); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| fn cycle(self) -> Cycle<Self> |
| where |
| Self: Sized + Clone, |
| { |
| Cycle::new(self) |
| } |
| |
| /// Sums the elements of an iterator. |
| /// |
| /// Takes each element, adds them together, and returns the result. |
| /// |
| /// An empty iterator returns the zero value of the type. |
| /// |
| /// # Panics |
| /// |
| /// When calling `sum()` and a primitive integer type is being returned, this |
| /// method will panic if the computation overflows and debug assertions are |
| /// enabled. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [1, 2, 3]; |
| /// let sum: i32 = a.iter().sum(); |
| /// |
| /// assert_eq!(sum, 6); |
| /// ``` |
| #[stable(feature = "iter_arith", since = "1.11.0")] |
| fn sum<S>(self) -> S |
| where |
| Self: Sized, |
| S: Sum<Self::Item>, |
| { |
| Sum::sum(self) |
| } |
| |
| /// Iterates over the entire iterator, multiplying all the elements |
| /// |
| /// An empty iterator returns the one value of the type. |
| /// |
| /// # Panics |
| /// |
| /// When calling `product()` and a primitive integer type is being returned, |
| /// method will panic if the computation overflows and debug assertions are |
| /// enabled. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// fn factorial(n: u32) -> u32 { |
| /// (1..=n).product() |
| /// } |
| /// assert_eq!(factorial(0), 1); |
| /// assert_eq!(factorial(1), 1); |
| /// assert_eq!(factorial(5), 120); |
| /// ``` |
| #[stable(feature = "iter_arith", since = "1.11.0")] |
| fn product<P>(self) -> P |
| where |
| Self: Sized, |
| P: Product<Self::Item>, |
| { |
| Product::product(self) |
| } |
| |
| /// Lexicographically compares the elements of this `Iterator` with those |
| /// of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal); |
| /// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less); |
| /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn cmp<I>(self, other: I) -> Ordering |
| where |
| I: IntoIterator<Item = Self::Item>, |
| Self::Item: Ord, |
| Self: Sized, |
| { |
| self.cmp_by(other, |x, y| x.cmp(&y)) |
| } |
| |
| /// Lexicographically compares the elements of this `Iterator` with those |
| /// of another with respect to the specified comparison function. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(iter_order_by)] |
| /// |
| /// use std::cmp::Ordering; |
| /// |
| /// let xs = [1, 2, 3, 4]; |
| /// let ys = [1, 4, 9, 16]; |
| /// |
| /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less); |
| /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal); |
| /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater); |
| /// ``` |
| #[unstable(feature = "iter_order_by", issue = "64295")] |
| fn cmp_by<I, F>(mut self, other: I, mut cmp: F) -> Ordering |
| where |
| Self: Sized, |
| I: IntoIterator, |
| F: FnMut(Self::Item, I::Item) -> Ordering, |
| { |
| let mut other = other.into_iter(); |
| |
| loop { |
| let x = match self.next() { |
| None => { |
| if other.next().is_none() { |
| return Ordering::Equal; |
| } else { |
| return Ordering::Less; |
| } |
| } |
| Some(val) => val, |
| }; |
| |
| let y = match other.next() { |
| None => return Ordering::Greater, |
| Some(val) => val, |
| }; |
| |
| match cmp(x, y) { |
| Ordering::Equal => (), |
| non_eq => return non_eq, |
| } |
| } |
| } |
| |
| /// Lexicographically compares the elements of this `Iterator` with those |
| /// of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal)); |
| /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less)); |
| /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater)); |
| /// |
| /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn partial_cmp<I>(self, other: I) -> Option<Ordering> |
| where |
| I: IntoIterator, |
| Self::Item: PartialOrd<I::Item>, |
| Self: Sized, |
| { |
| self.partial_cmp_by(other, |x, y| x.partial_cmp(&y)) |
| } |
| |
| /// Lexicographically compares the elements of this `Iterator` with those |
| /// of another with respect to the specified comparison function. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(iter_order_by)] |
| /// |
| /// use std::cmp::Ordering; |
| /// |
| /// let xs = [1.0, 2.0, 3.0, 4.0]; |
| /// let ys = [1.0, 4.0, 9.0, 16.0]; |
| /// |
| /// assert_eq!( |
| /// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)), |
| /// Some(Ordering::Less) |
| /// ); |
| /// assert_eq!( |
| /// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)), |
| /// Some(Ordering::Equal) |
| /// ); |
| /// assert_eq!( |
| /// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)), |
| /// Some(Ordering::Greater) |
| /// ); |
| /// ``` |
| #[unstable(feature = "iter_order_by", issue = "64295")] |
| fn partial_cmp_by<I, F>(mut self, other: I, mut partial_cmp: F) -> Option<Ordering> |
| where |
| Self: Sized, |
| I: IntoIterator, |
| F: FnMut(Self::Item, I::Item) -> Option<Ordering>, |
| { |
| let mut other = other.into_iter(); |
| |
| loop { |
| let x = match self.next() { |
| None => { |
| if other.next().is_none() { |
| return Some(Ordering::Equal); |
| } else { |
| return Some(Ordering::Less); |
| } |
| } |
| Some(val) => val, |
| }; |
| |
| let y = match other.next() { |
| None => return Some(Ordering::Greater), |
| Some(val) => val, |
| }; |
| |
| match partial_cmp(x, y) { |
| Some(Ordering::Equal) => (), |
| non_eq => return non_eq, |
| } |
| } |
| } |
| |
| /// Determines if the elements of this `Iterator` are equal to those of |
| /// another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().eq([1].iter()), true); |
| /// assert_eq!([1].iter().eq([1, 2].iter()), false); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn eq<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialEq<I::Item>, |
| Self: Sized, |
| { |
| self.eq_by(other, |x, y| x == y) |
| } |
| |
| /// Determines if the elements of this `Iterator` are equal to those of |
| /// another with respect to the specified equality function. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(iter_order_by)] |
| /// |
| /// let xs = [1, 2, 3, 4]; |
| /// let ys = [1, 4, 9, 16]; |
| /// |
| /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y)); |
| /// ``` |
| #[unstable(feature = "iter_order_by", issue = "64295")] |
| fn eq_by<I, F>(mut self, other: I, mut eq: F) -> bool |
| where |
| Self: Sized, |
| I: IntoIterator, |
| F: FnMut(Self::Item, I::Item) -> bool, |
| { |
| let mut other = other.into_iter(); |
| |
| loop { |
| let x = match self.next() { |
| None => return other.next().is_none(), |
| Some(val) => val, |
| }; |
| |
| let y = match other.next() { |
| None => return false, |
| Some(val) => val, |
| }; |
| |
| if !eq(x, y) { |
| return false; |
| } |
| } |
| } |
| |
| /// Determines if the elements of this `Iterator` are unequal to those of |
| /// another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().ne([1].iter()), false); |
| /// assert_eq!([1].iter().ne([1, 2].iter()), true); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn ne<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialEq<I::Item>, |
| Self: Sized, |
| { |
| !self.eq(other) |
| } |
| |
| /// Determines if the elements of this `Iterator` are lexicographically |
| /// less than those of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().lt([1].iter()), false); |
| /// assert_eq!([1].iter().lt([1, 2].iter()), true); |
| /// assert_eq!([1, 2].iter().lt([1].iter()), false); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn lt<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialOrd<I::Item>, |
| Self: Sized, |
| { |
| self.partial_cmp(other) == Some(Ordering::Less) |
| } |
| |
| /// Determines if the elements of this `Iterator` are lexicographically |
| /// less or equal to those of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().le([1].iter()), true); |
| /// assert_eq!([1].iter().le([1, 2].iter()), true); |
| /// assert_eq!([1, 2].iter().le([1].iter()), false); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn le<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialOrd<I::Item>, |
| Self: Sized, |
| { |
| matches!(self.partial_cmp(other), Some(Ordering::Less | Ordering::Equal)) |
| } |
| |
| /// Determines if the elements of this `Iterator` are lexicographically |
| /// greater than those of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().gt([1].iter()), false); |
| /// assert_eq!([1].iter().gt([1, 2].iter()), false); |
| /// assert_eq!([1, 2].iter().gt([1].iter()), true); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn gt<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialOrd<I::Item>, |
| Self: Sized, |
| { |
| self.partial_cmp(other) == Some(Ordering::Greater) |
| } |
| |
| /// Determines if the elements of this `Iterator` are lexicographically |
| /// greater than or equal to those of another. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!([1].iter().ge([1].iter()), true); |
| /// assert_eq!([1].iter().ge([1, 2].iter()), false); |
| /// assert_eq!([1, 2].iter().ge([1].iter()), true); |
| /// ``` |
| #[stable(feature = "iter_order", since = "1.5.0")] |
| fn ge<I>(self, other: I) -> bool |
| where |
| I: IntoIterator, |
| Self::Item: PartialOrd<I::Item>, |
| Self: Sized, |
| { |
| matches!(self.partial_cmp(other), Some(Ordering::Greater | Ordering::Equal)) |
| } |
| |
| /// Checks if the elements of this iterator are sorted. |
| /// |
| /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the |
| /// iterator yields exactly zero or one element, `true` is returned. |
| /// |
| /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition |
| /// implies that this function returns `false` if any two consecutive items are not |
| /// comparable. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(is_sorted)] |
| /// |
| /// assert!([1, 2, 2, 9].iter().is_sorted()); |
| /// assert!(![1, 3, 2, 4].iter().is_sorted()); |
| /// assert!([0].iter().is_sorted()); |
| /// assert!(std::iter::empty::<i32>().is_sorted()); |
| /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] |
| fn is_sorted(self) -> bool |
| where |
| Self: Sized, |
| Self::Item: PartialOrd, |
| { |
| self.is_sorted_by(PartialOrd::partial_cmp) |
| } |
| |
| /// Checks if the elements of this iterator are sorted using the given comparator function. |
| /// |
| /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` |
| /// function to determine the ordering of two elements. Apart from that, it's equivalent to |
| /// [`is_sorted`]; see its documentation for more information. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(is_sorted)] |
| /// |
| /// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b))); |
| /// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b))); |
| /// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b))); |
| /// assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| a.partial_cmp(b))); |
| /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b))); |
| /// ``` |
| /// |
| /// [`is_sorted`]: trait.Iterator.html#method.is_sorted |
| #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] |
| fn is_sorted_by<F>(mut self, mut compare: F) -> bool |
| where |
| Self: Sized, |
| F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>, |
| { |
| let mut last = match self.next() { |
| Some(e) => e, |
| None => return true, |
| }; |
| |
| while let Some(curr) = self.next() { |
| if let Some(Ordering::Greater) | None = compare(&last, &curr) { |
| return false; |
| } |
| last = curr; |
| } |
| |
| true |
| } |
| |
| /// Checks if the elements of this iterator are sorted using the given key extraction |
| /// function. |
| /// |
| /// Instead of comparing the iterator's elements directly, this function compares the keys of |
| /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see |
| /// its documentation for more information. |
| /// |
| /// [`is_sorted`]: trait.Iterator.html#method.is_sorted |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(is_sorted)] |
| /// |
| /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); |
| /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] |
| fn is_sorted_by_key<F, K>(self, f: F) -> bool |
| where |
| Self: Sized, |
| F: FnMut(Self::Item) -> K, |
| K: PartialOrd, |
| { |
| self.map(f).is_sorted() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<I: Iterator + ?Sized> Iterator for &mut I { |
| type Item = I::Item; |
| fn next(&mut self) -> Option<I::Item> { |
| (**self).next() |
| } |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| (**self).size_hint() |
| } |
| fn nth(&mut self, n: usize) -> Option<Self::Item> { |
| (**self).nth(n) |
| } |
| } |