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fuchsia / third_party / rust / refs/tags/0.11.0 / . / src / libcore / option.rs
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// 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
//! `int`. Notice that in order to use the inner `int` 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<int>> = None;
//! check_optional(&optional);
//!
//! let optional: Option<Box<int>> = Some(box 9000);
//! check_optional(&optional);
//!
//! fn check_optional(optional: &Option<Box<int>>) {
//! 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
//! match msg {
//! Some(ref m) => println!("{}", *m),
//! None => ()
//! }
//!
//! // Remove the contained string, destroying the Option
//! let unwrapped_msg = match msg {
//! Some(m) => m,
//! None => "default message"
//! };
//! ```
//!
//! Initialize a result to `None` before a loop:
//!
//! ```
//! enum Kingdom { Plant(uint, &'static str), Animal(uint, &'static str) }
//!
//! // A list of data to search through.
//! let all_the_big_things = [
//! Plant(250, "redwood"),
//! Plant(230, "noble fir"),
//! Plant(229, "sugar pine"),
//! Animal(25, "blue whale"),
//! Animal(19, "fin whale"),
//! 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.iter() {
//! match *big_thing {
//! 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);
//! }
//! Animal(..) | Plant(..) => ()
//! }
//! }
//!
//! match name_of_biggest_animal {
//! Some(name) => println!("the biggest animal is {}", name),
//! None => println!("there are no animals :(")
//! }
//! ```
use cmp::{PartialEq, Eq, Ord};
use default::Default;
use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
use mem;
use slice;
/// The `Option`
#[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
pub enum Option<T> {
/// No value
None,
/// Some value `T`
Some(T)
}
/////////////////////////////////////////////////////////////////////////////
// Type implementation
/////////////////////////////////////////////////////////////////////////////
impl<T> Option<T> {
/////////////////////////////////////////////////////////////////////////
// Querying the contained values
/////////////////////////////////////////////////////////////////////////
/// Returns `true` if the option is a `Some` value
#[inline]
pub fn is_some(&self) -> bool {
match *self {
Some(_) => true,
None => false
}
}
/// Returns `true` if the option is a `None` value
#[inline]
pub fn is_none(&self) -> bool {
!self.is_some()
}
/////////////////////////////////////////////////////////////////////////
// Adapter for working with references
/////////////////////////////////////////////////////////////////////////
/// Convert from `Option<T>` to `Option<&T>`
///
/// # Example
///
/// Convert an `Option<String>` into an `Option<int>`, 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<uint> = num_as_str.as_ref().map(|n| n.len());
/// println!("still can print num_as_str: {}", num_as_str);
/// ```
#[inline]
pub fn as_ref<'r>(&'r self) -> Option<&'r T> {
match *self { Some(ref x) => Some(x), None => None }
}
/// Convert from `Option<T>` to `Option<&mut T>`
#[inline]
pub fn as_mut<'r>(&'r mut self) -> Option<&'r mut T> {
match *self { Some(ref mut x) => Some(x), None => None }
}
/// Convert from `Option<T>` to `&[T]` (without copying)
#[inline]
pub fn as_slice<'r>(&'r self) -> &'r [T] {
match *self {
Some(ref x) => slice::ref_slice(x),
None => &[]
}
}
/// Convert from `Option<T>` to `&mut [T]` (without copying)
#[inline]
pub fn as_mut_slice<'r>(&'r mut self) -> &'r mut [T] {
match *self {
Some(ref mut x) => slice::mut_ref_slice(x),
None => &mut []
}
}
/////////////////////////////////////////////////////////////////////////
// Getting to contained values
/////////////////////////////////////////////////////////////////////////
/// Unwraps an option, yielding the content of a `Some`
///
/// # Failure
///
/// Fails if the value is a `None` with a custom failure message provided by
/// `msg`.
#[inline]
pub fn expect(self, msg: &str) -> T {
match self {
Some(val) => val,
None => fail!(msg),
}
}
/// Moves a value out of an option type and returns it, consuming the `Option`.
///
/// # Failure
///
/// Fails if the self value equals `None`.
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged.
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn unwrap(self) -> T {
match self {
Some(val) => val,
None => fail!("called `Option::unwrap()` on a `None` value"),
}
}
/// Returns the contained value or a default.
#[inline]
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.
#[inline]
pub fn unwrap_or_else(self, f: || -> T) -> 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
///
/// # Example
///
/// Convert an `Option<String>` into an `Option<uint>`, consuming the original:
///
/// ```
/// let num_as_str: Option<String> = Some("10".to_string());
/// // `Option::map` takes self *by value*, consuming `num_as_str`
/// let num_as_int: Option<uint> = num_as_str.map(|n| n.len());
/// ```
#[inline]
pub fn map<U>(self, f: |T| -> U) -> Option<U> {
match self { Some(x) => Some(f(x)), None => None }
}
/// Applies a function to the contained value or returns a default.
#[inline]
pub fn map_or<U>(self, def: U, f: |T| -> U) -> U {
match self { None => def, Some(t) => f(t) }
}
/// Applies a function to the contained value or does nothing.
/// Returns true if the contained value was mutated.
pub fn mutate(&mut self, f: |T| -> T) -> bool {
if self.is_some() {
*self = Some(f(self.take_unwrap()));
true
} else { false }
}
/// Applies a function to the contained value or sets it to a default.
/// Returns true if the contained value was mutated, or false if set to the default.
pub fn mutate_or_set(&mut self, def: T, f: |T| -> T) -> bool {
if self.is_some() {
*self = Some(f(self.take_unwrap()));
true
} else {
*self = Some(def);
false
}
}
/////////////////////////////////////////////////////////////////////////
// Iterator constructors
/////////////////////////////////////////////////////////////////////////
/// Returns an iterator over the possibly contained value.
#[inline]
pub fn iter<'r>(&'r self) -> Item<&'r T> {
Item{opt: self.as_ref()}
}
/// Returns a mutable iterator over the possibly contained value.
#[inline]
pub fn mut_iter<'r>(&'r mut self) -> Item<&'r mut T> {
Item{opt: self.as_mut()}
}
/// Returns a consuming iterator over the possibly contained value.
#[inline]
pub fn move_iter(self) -> Item<T> {
Item{opt: self}
}
/////////////////////////////////////////////////////////////////////////
// Boolean operations on the values, eager and lazy
/////////////////////////////////////////////////////////////////////////
/// Returns `None` if the option is `None`, otherwise returns `optb`.
#[inline]
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.
#[inline]
pub fn and_then<U>(self, f: |T| -> Option<U>) -> Option<U> {
match self {
Some(x) => f(x),
None => None,
}
}
/// Returns the option if it contains a value, otherwise returns `optb`.
#[inline]
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.
#[inline]
pub fn or_else(self, f: || -> Option<T>) -> Option<T> {
match self {
Some(_) => self,
None => f()
}
}
/////////////////////////////////////////////////////////////////////////
// Misc
/////////////////////////////////////////////////////////////////////////
/// Takes the value out of the option, leaving a `None` in its place.
#[inline]
pub fn take(&mut self) -> Option<T> {
mem::replace(self, None)
}
/// Filters an optional value using a given function.
#[inline(always)]
pub fn filtered(self, f: |t: &T| -> bool) -> Option<T> {
match self {
Some(x) => if f(&x) { Some(x) } else { None },
None => None
}
}
/// Applies a function zero or more times until the result is `None`.
#[inline]
pub fn while_some(self, f: |v: T| -> Option<T>) {
let mut opt = self;
loop {
match opt {
Some(x) => opt = f(x),
None => break
}
}
}
/////////////////////////////////////////////////////////////////////////
// Common special cases
/////////////////////////////////////////////////////////////////////////
/// The option dance. Moves a value out of an option type and returns it,
/// replacing the original with `None`.
///
/// # Failure
///
/// Fails if the value equals `None`.
#[inline]
pub fn take_unwrap(&mut self) -> T {
match self.take() {
Some(x) => x,
None => fail!("called `Option::take_unwrap()` on a `None` value")
}
}
/// Gets an immutable reference to the value inside an option.
///
/// # Failure
///
/// Fails if the value equals `None`
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged
/// (calling `get` on `None` is akin to dereferencing a null pointer).
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn get_ref<'a>(&'a self) -> &'a T {
match *self {
Some(ref x) => x,
None => fail!("called `Option::get_ref()` on a `None` value"),
}
}
/// Gets a mutable reference to the value inside an option.
///
/// # Failure
///
/// Fails if the value equals `None`
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged
/// (calling `get` on `None` is akin to dereferencing a null pointer).
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn get_mut_ref<'a>(&'a mut self) -> &'a mut T {
match *self {
Some(ref mut x) => x,
None => fail!("called `Option::get_mut_ref()` on a `None` value"),
}
}
}
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.
///
/// # Example
///
/// Convert a string to an integer, turning poorly-formed strings
/// into 0 (the default value for integers). `from_str` 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 = from_str(good_year_from_input).unwrap_or_default();
/// let bad_year = from_str(bad_year_from_input).unwrap_or_default();
///
/// assert_eq!(1909i, good_year);
/// assert_eq!(0i, bad_year);
/// ```
#[inline]
pub fn unwrap_or_default(self) -> T {
match self {
Some(x) => x,
None => Default::default()
}
}
}
/////////////////////////////////////////////////////////////////////////////
// Trait implementations
/////////////////////////////////////////////////////////////////////////////
impl<T> Default for Option<T> {
#[inline]
fn default() -> Option<T> { None }
}
/////////////////////////////////////////////////////////////////////////////
// The Option Iterator
/////////////////////////////////////////////////////////////////////////////
/// An `Option` iterator that yields either one or zero elements
///
/// The `Item` iterator is returned by the `iter`, `mut_iter` and `move_iter`
/// methods on `Option`.
#[deriving(Clone)]
pub struct Item<A> {
opt: Option<A>
}
impl<A> Iterator<A> for Item<A> {
#[inline]
fn next(&mut self) -> Option<A> {
self.opt.take()
}
#[inline]
fn size_hint(&self) -> (uint, Option<uint>) {
match self.opt {
Some(_) => (1, Some(1)),
None => (0, Some(0)),
}
}
}
impl<A> DoubleEndedIterator<A> for Item<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
self.opt.take()
}
}
impl<A> ExactSize<A> for Item<A> {}
/////////////////////////////////////////////////////////////////////////////
// Free functions
/////////////////////////////////////////////////////////////////////////////
/// 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
/// vector containing the values of each `Option` is returned.
///
/// Here is an example which increments every integer in a vector,
/// checking for overflow:
///
/// ```rust
/// use std::option;
/// use std::uint;
///
/// let v = vec!(1u, 2u);
/// let res: Option<Vec<uint>> = option::collect(v.iter().map(|x: &uint|
/// if *x == uint::MAX { None }
/// else { Some(x + 1) }
/// ));
/// assert!(res == Some(vec!(2u, 3u)));
/// ```
#[inline]
pub fn collect<T, Iter: Iterator<Option<T>>, V: FromIterator<T>>(iter: Iter) -> Option<V> {
// FIXME(#11084): This should be twice as fast once this bug is closed.
let mut iter = iter.scan(false, |state, x| {
match x {
Some(x) => Some(x),
None => {
*state = true;
None
}
}
});
let v: V = FromIterator::from_iter(iter.by_ref());
if iter.state {
None
} else {
Some(v)
}
}
/////////////////////////////////////////////////////////////////////////////
// Tests
/////////////////////////////////////////////////////////////////////////////
#[cfg(test)]
mod tests {
use realstd::vec::Vec;
use realstd::string::String;
use option::collect;
use prelude::*;
use realstd::str::{Str, StrAllocating};
use iter::range;
use str::StrSlice;
use kinds::marker;
use slice::ImmutableVector;
#[test]
fn test_get_ptr() {
unsafe {
let x = box 0;
let addr_x: *int = ::mem::transmute(&*x);
let opt = Some(x);
let y = opt.unwrap();
let addr_y: *int = ::mem::transmute(&*y);
assert_eq!(addr_x, addr_y);
}
}
#[test]
fn test_get_str() {
let x = "test".to_string();
let addr_x = x.as_slice().as_ptr();
let opt = Some(x);
let y = opt.unwrap();
let addr_y = y.as_slice().as_ptr();
assert_eq!(addr_x, addr_y);
}
#[test]
fn test_get_resource() {
use realstd::rc::Rc;
use cell::RefCell;
struct R {
i: Rc<RefCell<int>>,
}
#[unsafe_destructor]
impl ::ops::Drop for R {
fn drop(&mut self) {
let ii = &*self.i;
let i = *ii.borrow();
*ii.borrow_mut() = i + 1;
}
}
fn r(i: Rc<RefCell<int>>) -> R {
R {
i: i
}
}
fn realclone<T: ::realstd::clone::Clone>(t: &T) -> T {
use realstd::clone::Clone;
t.clone()
}
let i = Rc::new(RefCell::new(0i));
{
let x = r(realclone(&i));
let opt = Some(x);
let _y = opt.unwrap();
}
assert_eq!(*i.borrow(), 1);
}
#[test]
fn test_option_dance() {
let x = Some(());
let mut y = Some(5i);
let mut y2 = 0;
for _x in x.iter() {
y2 = y.take_unwrap();
}
assert_eq!(y2, 5);
assert!(y.is_none());
}
#[test] #[should_fail]
fn test_option_too_much_dance() {
let mut y = Some(marker::NoCopy);
let _y2 = y.take_unwrap();
let _y3 = y.take_unwrap();
}
#[test]
fn test_and() {
let x: Option<int> = Some(1i);
assert_eq!(x.and(Some(2i)), Some(2));
assert_eq!(x.and(None::<int>), None);
let x: Option<int> = None;
assert_eq!(x.and(Some(2i)), None);
assert_eq!(x.and(None::<int>), None);
}
#[test]
fn test_and_then() {
let x: Option<int> = Some(1);
assert_eq!(x.and_then(|x| Some(x + 1)), Some(2));
assert_eq!(x.and_then(|_| None::<int>), None);
let x: Option<int> = None;
assert_eq!(x.and_then(|x| Some(x + 1)), None);
assert_eq!(x.and_then(|_| None::<int>), None);
}
#[test]
fn test_or() {
let x: Option<int> = Some(1);
assert_eq!(x.or(Some(2)), Some(1));
assert_eq!(x.or(None), Some(1));
let x: Option<int> = None;
assert_eq!(x.or(Some(2)), Some(2));
assert_eq!(x.or(None), None);
}
#[test]
fn test_or_else() {
let x: Option<int> = Some(1);
assert_eq!(x.or_else(|| Some(2)), Some(1));
assert_eq!(x.or_else(|| None), Some(1));
let x: Option<int> = None;
assert_eq!(x.or_else(|| Some(2)), Some(2));
assert_eq!(x.or_else(|| None), None);
}
#[test]
fn test_option_while_some() {
let mut i = 0i;
Some(10).while_some(|j| {
i += 1;
if j > 0 {
Some(j-1)
} else {
None
}
});
assert_eq!(i, 11);
}
#[test]
fn test_unwrap() {
assert_eq!(Some(1i).unwrap(), 1);
let s = Some("hello".to_string()).unwrap();
assert_eq!(s.as_slice(), "hello");
}
#[test]
#[should_fail]
fn test_unwrap_fail1() {
let x: Option<int> = None;
x.unwrap();
}
#[test]
#[should_fail]
fn test_unwrap_fail2() {
let x: Option<String> = None;
x.unwrap();
}
#[test]
fn test_unwrap_or() {
let x: Option<int> = Some(1);
assert_eq!(x.unwrap_or(2), 1);
let x: Option<int> = None;
assert_eq!(x.unwrap_or(2), 2);
}
#[test]
fn test_unwrap_or_else() {
let x: Option<int> = Some(1);
assert_eq!(x.unwrap_or_else(|| 2), 1);
let x: Option<int> = None;
assert_eq!(x.unwrap_or_else(|| 2), 2);
}
#[test]
fn test_filtered() {
let some_stuff = Some(42i);
let modified_stuff = some_stuff.filtered(|&x| {x < 10});
assert_eq!(some_stuff.unwrap(), 42);
assert!(modified_stuff.is_none());
}
#[test]
fn test_iter() {
let val = 5i;
let x = Some(val);
let mut it = x.iter();
assert_eq!(it.size_hint(), (1, Some(1)));
assert_eq!(it.next(), Some(&val));
assert_eq!(it.size_hint(), (0, Some(0)));
assert!(it.next().is_none());
}
#[test]
fn test_mut_iter() {
let val = 5i;
let new_val = 11i;
let mut x = Some(val);
{
let mut it = x.mut_iter();
assert_eq!(it.size_hint(), (1, Some(1)));
match it.next() {
Some(interior) => {
assert_eq!(*interior, val);
*interior = new_val;
}
None => assert!(false),
}
assert_eq!(it.size_hint(), (0, Some(0)));
assert!(it.next().is_none());
}
assert_eq!(x, Some(new_val));
}
#[test]
fn test_ord() {
let small = Some(1.0f64);
let big = Some(5.0f64);
let nan = Some(0.0f64/0.0);
assert!(!(nan < big));
assert!(!(nan > big));
assert!(small < big);
assert!(None < big);
assert!(big > None);
}
#[test]
fn test_mutate() {
let mut x = Some(3i);
assert!(x.mutate(|i| i+1));
assert_eq!(x, Some(4i));
assert!(x.mutate_or_set(0, |i| i+1));
assert_eq!(x, Some(5i));
x = None;
assert!(!x.mutate(|i| i+1));
assert_eq!(x, None);
assert!(!x.mutate_or_set(0i, |i| i+1));
assert_eq!(x, Some(0i));
}
#[test]
fn test_collect() {
let v: Option<Vec<int>> = collect(range(0i, 0)
.map(|_| Some(0i)));
assert!(v == Some(vec![]));
let v: Option<Vec<int>> = collect(range(0i, 3)
.map(|x| Some(x)));
assert!(v == Some(vec![0, 1, 2]));
let v: Option<Vec<int>> = collect(range(0i, 3)
.map(|x| if x > 1 { None } else { Some(x) }));
assert!(v == None);
// test that it does not take more elements than it needs
let mut functions = [|| Some(()), || None, || fail!()];
let v: Option<Vec<()>> = collect(functions.mut_iter().map(|f| (*f)()));
assert!(v == None);
}
}