| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! Optional values. |
| //! |
| //! Type `Option` represents an optional value: every `Option` |
| //! is either `Some` and contains a value, or `None`, and |
| //! does not. `Option` types are very common in Rust code, as |
| //! they have a number of uses: |
| //! |
| //! * Initial values |
| //! * Return values for functions that are not defined |
| //! over their entire input range (partial functions) |
| //! * Return value for otherwise reporting simple errors, where `None` is |
| //! returned on error |
| //! * Optional struct fields |
| //! * Struct fields that can be loaned or "taken" |
| //! * Optional function arguments |
| //! * Nullable pointers |
| //! * Swapping things out of difficult situations |
| //! |
| //! Options are commonly paired with pattern matching to query the presence |
| //! of a value and take action, always accounting for the `None` case. |
| //! |
| //! ``` |
| //! fn divide(numerator: f64, denominator: f64) -> Option<f64> { |
| //! if denominator == 0.0 { |
| //! None |
| //! } else { |
| //! Some(numerator / denominator) |
| //! } |
| //! } |
| //! |
| //! // The return value of the function is an option |
| //! let result = divide(2.0, 3.0); |
| //! |
| //! // Pattern match to retrieve the value |
| //! match result { |
| //! // The division was valid |
| //! Some(x) => println!("Result: {}", x), |
| //! // The division was invalid |
| //! None => println!("Cannot divide by 0"), |
| //! } |
| //! ``` |
| //! |
| // |
| // FIXME: Show how `Option` is used in practice, with lots of methods |
| // |
| //! # Options and pointers ("nullable" pointers) |
| //! |
| //! Rust's pointer types must always point to a valid location; there are |
| //! no "null" pointers. Instead, Rust has *optional* pointers, like |
| //! the optional owned box, `Option<Box<T>>`. |
| //! |
| //! The following example uses `Option` to create an optional box of |
| //! `i32`. Notice that in order to use the inner `i32` value first the |
| //! `check_optional` function needs to use pattern matching to |
| //! determine whether the box has a value (i.e. it is `Some(...)`) or |
| //! not (`None`). |
| //! |
| //! ``` |
| //! let optional: Option<Box<i32>> = None; |
| //! check_optional(&optional); |
| //! |
| //! let optional: Option<Box<i32>> = Some(Box::new(9000)); |
| //! check_optional(&optional); |
| //! |
| //! fn check_optional(optional: &Option<Box<i32>>) { |
| //! match *optional { |
| //! Some(ref p) => println!("have value {}", p), |
| //! None => println!("have no value"), |
| //! } |
| //! } |
| //! ``` |
| //! |
| //! This usage of `Option` to create safe nullable pointers is so |
| //! common that Rust does special optimizations to make the |
| //! representation of `Option<Box<T>>` a single pointer. Optional pointers |
| //! in Rust are stored as efficiently as any other pointer type. |
| //! |
| //! # Examples |
| //! |
| //! Basic pattern matching on `Option`: |
| //! |
| //! ``` |
| //! let msg = Some("howdy"); |
| //! |
| //! // Take a reference to the contained string |
| //! if let Some(ref m) = msg { |
| //! println!("{}", *m); |
| //! } |
| //! |
| //! // Remove the contained string, destroying the Option |
| //! let unwrapped_msg = msg.unwrap_or("default message"); |
| //! ``` |
| //! |
| //! Initialize a result to `None` before a loop: |
| //! |
| //! ``` |
| //! enum Kingdom { Plant(u32, &'static str), Animal(u32, &'static str) } |
| //! |
| //! // A list of data to search through. |
| //! let all_the_big_things = [ |
| //! Kingdom::Plant(250, "redwood"), |
| //! Kingdom::Plant(230, "noble fir"), |
| //! Kingdom::Plant(229, "sugar pine"), |
| //! Kingdom::Animal(25, "blue whale"), |
| //! Kingdom::Animal(19, "fin whale"), |
| //! Kingdom::Animal(15, "north pacific right whale"), |
| //! ]; |
| //! |
| //! // We're going to search for the name of the biggest animal, |
| //! // but to start with we've just got `None`. |
| //! let mut name_of_biggest_animal = None; |
| //! let mut size_of_biggest_animal = 0; |
| //! for big_thing in &all_the_big_things { |
| //! match *big_thing { |
| //! Kingdom::Animal(size, name) if size > size_of_biggest_animal => { |
| //! // Now we've found the name of some big animal |
| //! size_of_biggest_animal = size; |
| //! name_of_biggest_animal = Some(name); |
| //! } |
| //! Kingdom::Animal(..) | Kingdom::Plant(..) => () |
| //! } |
| //! } |
| //! |
| //! match name_of_biggest_animal { |
| //! Some(name) => println!("the biggest animal is {}", name), |
| //! None => println!("there are no animals :("), |
| //! } |
| //! ``` |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use self::Option::*; |
| |
| use clone::Clone; |
| use convert::From; |
| use default::Default; |
| use iter::ExactSizeIterator; |
| use iter::{Iterator, DoubleEndedIterator, FromIterator, IntoIterator}; |
| use mem; |
| use ops::FnOnce; |
| use result::Result::{Ok, Err}; |
| use result::Result; |
| |
| // Note that this is not a lang item per se, but it has a hidden dependency on |
| // `Iterator`, which is one. The compiler assumes that the `next` method of |
| // `Iterator` is an enumeration with one type parameter and two variants, |
| // which basically means it must be `Option`. |
| |
| /// The `Option` type. See [the module level documentation](index.html) for more. |
| #[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub enum Option<T> { |
| /// No value |
| #[stable(feature = "rust1", since = "1.0.0")] |
| None, |
| /// Some value `T` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| Some(#[stable(feature = "rust1", since = "1.0.0")] T) |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Type implementation |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| impl<T> Option<T> { |
| ///////////////////////////////////////////////////////////////////////// |
| // Querying the contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns `true` if the option is a `Some` value |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x: Option<u32> = Some(2); |
| /// assert_eq!(x.is_some(), true); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.is_some(), false); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn is_some(&self) -> bool { |
| match *self { |
| Some(_) => true, |
| None => false, |
| } |
| } |
| |
| /// Returns `true` if the option is a `None` value |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x: Option<u32> = Some(2); |
| /// assert_eq!(x.is_none(), false); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.is_none(), true); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn is_none(&self) -> bool { |
| !self.is_some() |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Adapter for working with references |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Converts from `Option<T>` to `Option<&T>` |
| /// |
| /// # Examples |
| /// |
| /// Convert an `Option<String>` into an `Option<usize>`, preserving the original. |
| /// The `map` method takes the `self` argument by value, consuming the original, |
| /// so this technique uses `as_ref` to first take an `Option` to a reference |
| /// to the value inside the original. |
| /// |
| /// ``` |
| /// let num_as_str: Option<String> = Some("10".to_string()); |
| /// // First, cast `Option<String>` to `Option<&String>` with `as_ref`, |
| /// // then consume *that* with `map`, leaving `num_as_str` on the stack. |
| /// let num_as_int: Option<usize> = num_as_str.as_ref().map(|n| n.len()); |
| /// println!("still can print num_as_str: {:?}", num_as_str); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn as_ref(&self) -> Option<&T> { |
| match *self { |
| Some(ref x) => Some(x), |
| None => None, |
| } |
| } |
| |
| /// Converts from `Option<T>` to `Option<&mut T>` |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(2); |
| /// match x.as_mut() { |
| /// Some(v) => *v = 42, |
| /// None => {}, |
| /// } |
| /// assert_eq!(x, Some(42)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn as_mut(&mut self) -> Option<&mut T> { |
| match *self { |
| Some(ref mut x) => Some(x), |
| None => None, |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Getting to contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Unwraps an option, yielding the content of a `Some`. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the value is a `None` with a custom panic message provided by |
| /// `msg`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("value"); |
| /// assert_eq!(x.expect("the world is ending"), "value"); |
| /// ``` |
| /// |
| /// ```{.should_panic} |
| /// let x: Option<&str> = None; |
| /// x.expect("the world is ending"); // panics with `the world is ending` |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn expect(self, msg: &str) -> T { |
| match self { |
| Some(val) => val, |
| None => expect_failed(msg), |
| } |
| } |
| |
| /// Moves the value `v` out of the `Option<T>` if it is `Some(v)`. |
| /// |
| /// # Panics |
| /// |
| /// Panics if the self value equals `None`. |
| /// |
| /// # Safety note |
| /// |
| /// In general, because this function may panic, its use is discouraged. |
| /// Instead, prefer to use pattern matching and handle the `None` |
| /// case explicitly. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("air"); |
| /// assert_eq!(x.unwrap(), "air"); |
| /// ``` |
| /// |
| /// ```{.should_panic} |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.unwrap(), "air"); // fails |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap(self) -> T { |
| match self { |
| Some(val) => val, |
| None => panic!("called `Option::unwrap()` on a `None` value"), |
| } |
| } |
| |
| /// Returns the contained value or a default. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!(Some("car").unwrap_or("bike"), "car"); |
| /// assert_eq!(None.unwrap_or("bike"), "bike"); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or(self, def: T) -> T { |
| match self { |
| Some(x) => x, |
| None => def, |
| } |
| } |
| |
| /// Returns the contained value or computes it from a closure. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let k = 10; |
| /// assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4); |
| /// assert_eq!(None.unwrap_or_else(|| 2 * k), 20); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T { |
| match self { |
| Some(x) => x, |
| None => f(), |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Transforming contained values |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value |
| /// |
| /// # Examples |
| /// |
| /// Convert an `Option<String>` into an `Option<usize>`, consuming the original: |
| /// |
| /// ``` |
| /// let maybe_some_string = Some(String::from("Hello, World!")); |
| /// // `Option::map` takes self *by value*, consuming `maybe_some_string` |
| /// let maybe_some_len = maybe_some_string.map(|s| s.len()); |
| /// |
| /// assert_eq!(maybe_some_len, Some(13)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> { |
| match self { |
| Some(x) => Some(f(x)), |
| None => None, |
| } |
| } |
| |
| /// Applies a function to the contained value (if any), |
| /// or returns a `default` (if not). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.map_or(42, |v| v.len()), 3); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.map_or(42, |v| v.len()), 42); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U { |
| match self { |
| Some(t) => f(t), |
| None => default, |
| } |
| } |
| |
| /// Applies a function to the contained value (if any), |
| /// or computes a `default` (if not). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let k = 21; |
| /// |
| /// let x = Some("foo"); |
| /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn map_or_else<U, D: FnOnce() -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U { |
| match self { |
| Some(t) => f(t), |
| None => default(), |
| } |
| } |
| |
| /// Transforms the `Option<T>` into a `Result<T, E>`, mapping `Some(v)` to |
| /// `Ok(v)` and `None` to `Err(err)`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.ok_or(0), Ok("foo")); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.ok_or(0), Err(0)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn ok_or<E>(self, err: E) -> Result<T, E> { |
| match self { |
| Some(v) => Ok(v), |
| None => Err(err), |
| } |
| } |
| |
| /// Transforms the `Option<T>` into a `Result<T, E>`, mapping `Some(v)` to |
| /// `Ok(v)` and `None` to `Err(err())`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("foo"); |
| /// assert_eq!(x.ok_or_else(|| 0), Ok("foo")); |
| /// |
| /// let x: Option<&str> = None; |
| /// assert_eq!(x.ok_or_else(|| 0), Err(0)); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> { |
| match self { |
| Some(v) => Ok(v), |
| None => Err(err()), |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Iterator constructors |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns an iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(4); |
| /// assert_eq!(x.iter().next(), Some(&4)); |
| /// |
| /// let x: Option<u32> = None; |
| /// assert_eq!(x.iter().next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn iter(&self) -> Iter<T> { |
| Iter { inner: Item { opt: self.as_ref() } } |
| } |
| |
| /// Returns a mutable iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(4); |
| /// match x.iter_mut().next() { |
| /// Some(v) => *v = 42, |
| /// None => {}, |
| /// } |
| /// assert_eq!(x, Some(42)); |
| /// |
| /// let mut x: Option<u32> = None; |
| /// assert_eq!(x.iter_mut().next(), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn iter_mut(&mut self) -> IterMut<T> { |
| IterMut { inner: Item { opt: self.as_mut() } } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Boolean operations on the values, eager and lazy |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Returns `None` if the option is `None`, otherwise returns `optb`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(2); |
| /// let y: Option<&str> = None; |
| /// assert_eq!(x.and(y), None); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y = Some("foo"); |
| /// assert_eq!(x.and(y), None); |
| /// |
| /// let x = Some(2); |
| /// let y = Some("foo"); |
| /// assert_eq!(x.and(y), Some("foo")); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y: Option<&str> = None; |
| /// assert_eq!(x.and(y), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn and<U>(self, optb: Option<U>) -> Option<U> { |
| match self { |
| Some(_) => optb, |
| None => None, |
| } |
| } |
| |
| /// Returns `None` if the option is `None`, otherwise calls `f` with the |
| /// wrapped value and returns the result. |
| /// |
| /// Some languages call this operation flatmap. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// fn sq(x: u32) -> Option<u32> { Some(x * x) } |
| /// fn nope(_: u32) -> Option<u32> { None } |
| /// |
| /// assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16)); |
| /// assert_eq!(Some(2).and_then(sq).and_then(nope), None); |
| /// assert_eq!(Some(2).and_then(nope).and_then(sq), None); |
| /// assert_eq!(None.and_then(sq).and_then(sq), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn and_then<U, F: FnOnce(T) -> Option<U>>(self, f: F) -> Option<U> { |
| match self { |
| Some(x) => f(x), |
| None => None, |
| } |
| } |
| |
| /// Returns the option if it contains a value, otherwise returns `optb`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some(2); |
| /// let y = None; |
| /// assert_eq!(x.or(y), Some(2)); |
| /// |
| /// let x = None; |
| /// let y = Some(100); |
| /// assert_eq!(x.or(y), Some(100)); |
| /// |
| /// let x = Some(2); |
| /// let y = Some(100); |
| /// assert_eq!(x.or(y), Some(2)); |
| /// |
| /// let x: Option<u32> = None; |
| /// let y = None; |
| /// assert_eq!(x.or(y), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn or(self, optb: Option<T>) -> Option<T> { |
| match self { |
| Some(_) => self, |
| None => optb, |
| } |
| } |
| |
| /// Returns the option if it contains a value, otherwise calls `f` and |
| /// returns the result. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// fn nobody() -> Option<&'static str> { None } |
| /// fn vikings() -> Option<&'static str> { Some("vikings") } |
| /// |
| /// assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians")); |
| /// assert_eq!(None.or_else(vikings), Some("vikings")); |
| /// assert_eq!(None.or_else(nobody), None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T> { |
| match self { |
| Some(_) => self, |
| None => f(), |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////// |
| // Misc |
| ///////////////////////////////////////////////////////////////////////// |
| |
| /// Takes the value out of the option, leaving a `None` in its place. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let mut x = Some(2); |
| /// x.take(); |
| /// assert_eq!(x, None); |
| /// |
| /// let mut x: Option<u32> = None; |
| /// x.take(); |
| /// assert_eq!(x, None); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn take(&mut self) -> Option<T> { |
| mem::replace(self, None) |
| } |
| } |
| |
| impl<'a, T: Clone> Option<&'a T> { |
| /// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the |
| /// option. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn cloned(self) -> Option<T> { |
| self.map(|t| t.clone()) |
| } |
| } |
| |
| impl<T: Default> Option<T> { |
| /// Returns the contained value or a default |
| /// |
| /// Consumes the `self` argument then, if `Some`, returns the contained |
| /// value, otherwise if `None`, returns the default value for that |
| /// type. |
| /// |
| /// # Examples |
| /// |
| /// Convert a string to an integer, turning poorly-formed strings |
| /// into 0 (the default value for integers). `parse` converts |
| /// a string to any other type that implements `FromStr`, returning |
| /// `None` on error. |
| /// |
| /// ``` |
| /// let good_year_from_input = "1909"; |
| /// let bad_year_from_input = "190blarg"; |
| /// let good_year = good_year_from_input.parse().ok().unwrap_or_default(); |
| /// let bad_year = bad_year_from_input.parse().ok().unwrap_or_default(); |
| /// |
| /// assert_eq!(1909, good_year); |
| /// assert_eq!(0, bad_year); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub fn unwrap_or_default(self) -> T { |
| match self { |
| Some(x) => x, |
| None => Default::default(), |
| } |
| } |
| } |
| |
| // This is a separate function to reduce the code size of .expect() itself. |
| #[inline(never)] |
| #[cold] |
| fn expect_failed(msg: &str) -> ! { |
| panic!("{}", msg) |
| } |
| |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // Trait implementations |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T> Default for Option<T> { |
| #[inline] |
| fn default() -> Option<T> { None } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T> IntoIterator for Option<T> { |
| type Item = T; |
| type IntoIter = IntoIter<T>; |
| |
| /// Returns a consuming iterator over the possibly contained value. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let x = Some("string"); |
| /// let v: Vec<&str> = x.into_iter().collect(); |
| /// assert_eq!(v, ["string"]); |
| /// |
| /// let x = None; |
| /// let v: Vec<&str> = x.into_iter().collect(); |
| /// assert!(v.is_empty()); |
| /// ``` |
| #[inline] |
| fn into_iter(self) -> IntoIter<T> { |
| IntoIter { inner: Item { opt: self } } |
| } |
| } |
| |
| #[stable(since = "1.4.0", feature = "option_iter")] |
| impl<'a, T> IntoIterator for &'a Option<T> { |
| type Item = &'a T; |
| type IntoIter = Iter<'a, T>; |
| |
| fn into_iter(self) -> Iter<'a, T> { |
| self.iter() |
| } |
| } |
| |
| #[stable(since = "1.4.0", feature = "option_iter")] |
| impl<'a, T> IntoIterator for &'a mut Option<T> { |
| type Item = &'a mut T; |
| type IntoIter = IterMut<'a, T>; |
| |
| fn into_iter(mut self) -> IterMut<'a, T> { |
| self.iter_mut() |
| } |
| } |
| |
| #[stable(since = "1.12.0", feature = "option_from")] |
| impl<T> From<T> for Option<T> { |
| fn from(val: T) -> Option<T> { |
| Some(val) |
| } |
| } |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // The Option Iterators |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[derive(Clone, Debug)] |
| struct Item<A> { |
| opt: Option<A> |
| } |
| |
| impl<A> Iterator for Item<A> { |
| type Item = A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<A> { |
| self.opt.take() |
| } |
| |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| match self.opt { |
| Some(_) => (1, Some(1)), |
| None => (0, Some(0)), |
| } |
| } |
| } |
| |
| impl<A> DoubleEndedIterator for Item<A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<A> { |
| self.opt.take() |
| } |
| } |
| |
| impl<A> ExactSizeIterator for Item<A> {} |
| |
| /// An iterator over a reference of the contained item in an Option. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[derive(Debug)] |
| pub struct Iter<'a, A: 'a> { inner: Item<&'a A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> Iterator for Iter<'a, A> { |
| type Item = &'a A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<&'a A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> DoubleEndedIterator for Iter<'a, A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<&'a A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> ExactSizeIterator for Iter<'a, A> {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> Clone for Iter<'a, A> { |
| fn clone(&self) -> Iter<'a, A> { |
| Iter { inner: self.inner.clone() } |
| } |
| } |
| |
| /// An iterator over a mutable reference of the contained item in an Option. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[derive(Debug)] |
| pub struct IterMut<'a, A: 'a> { inner: Item<&'a mut A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> Iterator for IterMut<'a, A> { |
| type Item = &'a mut A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<&'a mut A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> DoubleEndedIterator for IterMut<'a, A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<&'a mut A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<'a, A> ExactSizeIterator for IterMut<'a, A> {} |
| |
| /// An iterator over the item contained inside an Option. |
| #[derive(Clone, Debug)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct IntoIter<A> { inner: Item<A> } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> Iterator for IntoIter<A> { |
| type Item = A; |
| |
| #[inline] |
| fn next(&mut self) -> Option<A> { self.inner.next() } |
| #[inline] |
| fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> DoubleEndedIterator for IntoIter<A> { |
| #[inline] |
| fn next_back(&mut self) -> Option<A> { self.inner.next_back() } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A> ExactSizeIterator for IntoIter<A> {} |
| |
| ///////////////////////////////////////////////////////////////////////////// |
| // FromIterator |
| ///////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> { |
| /// Takes each element in the `Iterator`: if it is `None`, no further |
| /// elements are taken, and the `None` is returned. Should no `None` occur, a |
| /// container with the values of each `Option` is returned. |
| /// |
| /// Here is an example which increments every integer in a vector, |
| /// checking for overflow: |
| /// |
| /// ``` |
| /// use std::u16; |
| /// |
| /// let v = vec!(1, 2); |
| /// let res: Option<Vec<u16>> = v.iter().map(|&x: &u16| |
| /// if x == u16::MAX { None } |
| /// else { Some(x + 1) } |
| /// ).collect(); |
| /// assert!(res == Some(vec!(2, 3))); |
| /// ``` |
| #[inline] |
| fn from_iter<I: IntoIterator<Item=Option<A>>>(iter: I) -> Option<V> { |
| // FIXME(#11084): This could be replaced with Iterator::scan when this |
| // performance bug is closed. |
| |
| struct Adapter<Iter> { |
| iter: Iter, |
| found_none: bool, |
| } |
| |
| impl<T, Iter: Iterator<Item=Option<T>>> Iterator for Adapter<Iter> { |
| type Item = T; |
| |
| #[inline] |
| fn next(&mut self) -> Option<T> { |
| match self.iter.next() { |
| Some(Some(value)) => Some(value), |
| Some(None) => { |
| self.found_none = true; |
| None |
| } |
| None => None, |
| } |
| } |
| } |
| |
| let mut adapter = Adapter { iter: iter.into_iter(), found_none: false }; |
| let v: V = FromIterator::from_iter(adapter.by_ref()); |
| |
| if adapter.found_none { |
| None |
| } else { |
| Some(v) |
| } |
| } |
| } |