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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
//!
//! [`Option`]s 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(...)`][`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!("has value {}", p),
//! None => println!("has 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 :("),
//! }
//! ```
//!
//! [`Option`]: enum.Option.html
//! [`Some`]: enum.Option.html#variant.Some
//! [`None`]: enum.Option.html#variant.None
//! [`Box<T>`]: ../../std/boxed/struct.Box.html
//! [`i32`]: ../../std/primitive.i32.html
#![stable(feature = "rust1", since = "1.0.0")]
use iter::{FromIterator, FusedIterator, TrustedLen};
use mem;
// 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.
///
/// [`map`]: enum.Option.html#method.map
///
/// ```
/// 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)`.
///
/// In general, because this function may panic, its use is discouraged.
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
///
/// # Panics
///
/// Panics if the self value equals `None`.
///
/// # 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)`][Err].
///
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
/// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok
/// [Err]: ../../std/result/enum.Result.html#variant.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())`][Err].
///
/// [`Result<T, E>`]: ../../std/result/enum.Result.html
/// [`Ok(v)`]: ../../std/result/enum.Result.html#variant.Ok
/// [Err]: ../../std/result/enum.Result.html#variant.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(),
}
}
/////////////////////////////////////////////////////////////////////////
// Entry-like operations to insert if None and return a reference
/////////////////////////////////////////////////////////////////////////
/// Inserts `v` into the option if it is `None`, then
/// returns a mutable reference to the contained value.
///
/// # Examples
///
/// ```
/// #![feature(option_entry)]
///
/// let mut x = None;
///
/// {
/// let y: &mut u32 = x.get_or_insert(5);
/// assert_eq!(y, &5);
///
/// *y = 7;
/// }
///
/// assert_eq!(x, Some(7));
/// ```
#[inline]
#[unstable(feature = "option_entry", issue = "39288")]
pub fn get_or_insert(&mut self, v: T) -> &mut T {
match *self {
None => *self = Some(v),
_ => (),
}
match *self {
Some(ref mut v) => v,
_ => unreachable!(),
}
}
/// Inserts a value computed from `f` into the option if it is `None`, then
/// returns a mutable reference to the contained value.
///
/// # Examples
///
/// ```
/// #![feature(option_entry)]
///
/// let mut x = None;
///
/// {
/// let y: &mut u32 = x.get_or_insert_with(|| 5);
/// assert_eq!(y, &5);
///
/// *y = 7;
/// }
///
/// assert_eq!(x, Some(7));
/// ```
#[inline]
#[unstable(feature = "option_entry", issue = "39288")]
pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T {
match *self {
None => *self = Some(f()),
_ => (),
}
match *self {
Some(ref mut v) => v,
_ => unreachable!(),
}
}
/////////////////////////////////////////////////////////////////////////
// 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.
///
/// # Examples
///
/// ```
/// let x = 12;
/// let opt_x = Some(&x);
/// assert_eq!(opt_x, Some(&12));
/// let cloned = opt_x.cloned();
/// assert_eq!(cloned, Some(12));
/// ```
#[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> {
/// Returns None.
#[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> {}
impl<A> FusedIterator for Item<A> {}
unsafe impl<A> TrustedLen for Item<A> {}
/// An iterator over a reference of the contained item in an [`Option`].
///
/// [`Option`]: enum.Option.html
#[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> {}
#[unstable(feature = "fused", issue = "35602")]
impl<'a, A> FusedIterator for Iter<'a, A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<'a, A> TrustedLen 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`].
///
/// [`Option`]: enum.Option.html
#[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> {}
#[unstable(feature = "fused", issue = "35602")]
impl<'a, A> FusedIterator for IterMut<'a, A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<'a, A> TrustedLen for IterMut<'a, A> {}
/// An iterator over the item contained inside an [`Option`].
///
/// [`Option`]: enum.Option.html
#[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> {}
#[unstable(feature = "fused", issue = "35602")]
impl<A> FusedIterator for IntoIter<A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A> TrustedLen 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)
}
}
}