//! // Pattern match to retrieve the value
//! match result {
//! // The division was valid
-//! Some(x) => println!("Result: {}", x),
+//! Some(x) => println!("Result: {x}"),
//! // The division was invalid
//! None => println!("Cannot divide by 0"),
//! }
//!
//! Rust's pointer types must always point to a valid location; there are
//! no "null" references. Instead, Rust has *optional* pointers, like
-//! the optional owned box, [`Option`]`<`[`Box<T>`]`>`.
+//! the optional owned box, <code>[Option]<[Box\<T>]></code>.
+//!
+//! [Box\<T>]: ../../std/boxed/struct.Box.html
//!
//! 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
+//! [`i32`]. Notice that in order to use the inner [`i32`] value, the
+//! `check_optional` function first needs to use pattern matching to
//! determine whether the box has a value (i.e., it is [`Some(...)`][`Some`]) or
//! not ([`None`]).
//!
//!
//! fn check_optional(optional: Option<Box<i32>>) {
//! match optional {
-//! Some(p) => println!("has value {}", p),
+//! Some(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.
+//! # Representation
+//!
+//! Rust guarantees to optimize the following types `T` such that
+//! [`Option<T>`] has the same size as `T`:
+//!
+//! * [`Box<U>`]
+//! * `&U`
+//! * `&mut U`
+//! * `fn`, `extern "C" fn`[^extern_fn]
+//! * [`num::NonZero*`]
+//! * [`ptr::NonNull<U>`]
+//! * `#[repr(transparent)]` struct around one of the types in this list.
+//!
+//! [^extern_fn]: this remains true for any other ABI: `extern "abi" fn` (_e.g._, `extern "system" fn`)
+//!
+//! [`Box<U>`]: ../../std/boxed/struct.Box.html
+//! [`num::NonZero*`]: crate::num
+//! [`ptr::NonNull<U>`]: crate::ptr::NonNull
+//!
+//! This is called the "null pointer optimization" or NPO.
+//!
+//! It is further guaranteed that, for the cases above, one can
+//! [`mem::transmute`] from all valid values of `T` to `Option<T>` and
+//! from `Some::<T>(_)` to `T` (but transmuting `None::<T>` to `T`
+//! is undefined behaviour).
+//!
+//! # Method overview
+//!
+//! In addition to working with pattern matching, [`Option`] provides a wide
+//! variety of different methods.
+//!
+//! ## Querying the variant
+//!
+//! The [`is_some`] and [`is_none`] methods return [`true`] if the [`Option`]
+//! is [`Some`] or [`None`], respectively.
+//!
+//! [`is_none`]: Option::is_none
+//! [`is_some`]: Option::is_some
+//!
+//! ## Adapters for working with references
+//!
+//! * [`as_ref`] converts from <code>[&][][Option]\<T></code> to <code>[Option]<[&]T></code>
+//! * [`as_mut`] converts from <code>[&mut] [Option]\<T></code> to <code>[Option]<[&mut] T></code>
+//! * [`as_deref`] converts from <code>[&][][Option]\<T></code> to
+//! <code>[Option]<[&]T::[Target]></code>
+//! * [`as_deref_mut`] converts from <code>[&mut] [Option]\<T></code> to
+//! <code>[Option]<[&mut] T::[Target]></code>
+//! * [`as_pin_ref`] converts from <code>[Pin]<[&][][Option]\<T>></code> to
+//! <code>[Option]<[Pin]<[&]T>></code>
+//! * [`as_pin_mut`] converts from <code>[Pin]<[&mut] [Option]\<T>></code> to
+//! <code>[Option]<[Pin]<[&mut] T>></code>
+//!
+//! [&]: reference "shared reference"
+//! [&mut]: reference "mutable reference"
+//! [Target]: Deref::Target "ops::Deref::Target"
+//! [`as_deref`]: Option::as_deref
+//! [`as_deref_mut`]: Option::as_deref_mut
+//! [`as_mut`]: Option::as_mut
+//! [`as_pin_mut`]: Option::as_pin_mut
+//! [`as_pin_ref`]: Option::as_pin_ref
+//! [`as_ref`]: Option::as_ref
+//!
+//! ## Extracting the contained value
+//!
+//! These methods extract the contained value in an [`Option<T>`] when it
+//! is the [`Some`] variant. If the [`Option`] is [`None`]:
+//!
+//! * [`expect`] panics with a provided custom message
+//! * [`unwrap`] panics with a generic message
+//! * [`unwrap_or`] returns the provided default value
+//! * [`unwrap_or_default`] returns the default value of the type `T`
+//! (which must implement the [`Default`] trait)
+//! * [`unwrap_or_else`] returns the result of evaluating the provided
+//! function
+//!
+//! [`expect`]: Option::expect
+//! [`unwrap`]: Option::unwrap
+//! [`unwrap_or`]: Option::unwrap_or
+//! [`unwrap_or_default`]: Option::unwrap_or_default
+//! [`unwrap_or_else`]: Option::unwrap_or_else
+//!
+//! ## Transforming contained values
+//!
+//! These methods transform [`Option`] to [`Result`]:
+//!
+//! * [`ok_or`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to
+//! [`Err(err)`] using the provided default `err` value
+//! * [`ok_or_else`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to
+//! a value of [`Err`] using the provided function
+//! * [`transpose`] transposes an [`Option`] of a [`Result`] into a
+//! [`Result`] of an [`Option`]
+//!
+//! [`Err(err)`]: Err
+//! [`Ok(v)`]: Ok
+//! [`Some(v)`]: Some
+//! [`ok_or`]: Option::ok_or
+//! [`ok_or_else`]: Option::ok_or_else
+//! [`transpose`]: Option::transpose
+//!
+//! These methods transform the [`Some`] variant:
+//!
+//! * [`filter`] calls the provided predicate function on the contained
+//! value `t` if the [`Option`] is [`Some(t)`], and returns [`Some(t)`]
+//! if the function returns `true`; otherwise, returns [`None`]
+//! * [`flatten`] removes one level of nesting from an
+//! [`Option<Option<T>>`]
+//! * [`map`] transforms [`Option<T>`] to [`Option<U>`] by applying the
+//! provided function to the contained value of [`Some`] and leaving
+//! [`None`] values unchanged
+//!
+//! [`Some(t)`]: Some
+//! [`filter`]: Option::filter
+//! [`flatten`]: Option::flatten
+//! [`map`]: Option::map
+//!
+//! These methods transform [`Option<T>`] to a value of a possibly
+//! different type `U`:
+//!
+//! * [`map_or`] applies the provided function to the contained value of
+//! [`Some`], or returns the provided default value if the [`Option`] is
+//! [`None`]
+//! * [`map_or_else`] applies the provided function to the contained value
+//! of [`Some`], or returns the result of evaluating the provided
+//! fallback function if the [`Option`] is [`None`]
+//!
+//! [`map_or`]: Option::map_or
+//! [`map_or_else`]: Option::map_or_else
+//!
+//! These methods combine the [`Some`] variants of two [`Option`] values:
+//!
+//! * [`zip`] returns [`Some((s, o))`] if `self` is [`Some(s)`] and the
+//! provided [`Option`] value is [`Some(o)`]; otherwise, returns [`None`]
+//! * [`zip_with`] calls the provided function `f` and returns
+//! [`Some(f(s, o))`] if `self` is [`Some(s)`] and the provided
+//! [`Option`] value is [`Some(o)`]; otherwise, returns [`None`]
+//!
+//! [`Some(f(s, o))`]: Some
+//! [`Some(o)`]: Some
+//! [`Some(s)`]: Some
+//! [`Some((s, o))`]: Some
+//! [`zip`]: Option::zip
+//! [`zip_with`]: Option::zip_with
+//!
+//! ## Boolean operators
+//!
+//! These methods treat the [`Option`] as a boolean value, where [`Some`]
+//! acts like [`true`] and [`None`] acts like [`false`]. There are two
+//! categories of these methods: ones that take an [`Option`] as input, and
+//! ones that take a function as input (to be lazily evaluated).
+//!
+//! The [`and`], [`or`], and [`xor`] methods take another [`Option`] as
+//! input, and produce an [`Option`] as output. Only the [`and`] method can
+//! produce an [`Option<U>`] value having a different inner type `U` than
+//! [`Option<T>`].
+//!
+//! | method | self | input | output |
+//! |---------|-----------|-----------|-----------|
+//! | [`and`] | `None` | (ignored) | `None` |
+//! | [`and`] | `Some(x)` | `None` | `None` |
+//! | [`and`] | `Some(x)` | `Some(y)` | `Some(y)` |
+//! | [`or`] | `None` | `None` | `None` |
+//! | [`or`] | `None` | `Some(y)` | `Some(y)` |
+//! | [`or`] | `Some(x)` | (ignored) | `Some(x)` |
+//! | [`xor`] | `None` | `None` | `None` |
+//! | [`xor`] | `None` | `Some(y)` | `Some(y)` |
+//! | [`xor`] | `Some(x)` | `None` | `Some(x)` |
+//! | [`xor`] | `Some(x)` | `Some(y)` | `None` |
+//!
+//! [`and`]: Option::and
+//! [`or`]: Option::or
+//! [`xor`]: Option::xor
+//!
+//! The [`and_then`] and [`or_else`] methods take a function as input, and
+//! only evaluate the function when they need to produce a new value. Only
+//! the [`and_then`] method can produce an [`Option<U>`] value having a
+//! different inner type `U` than [`Option<T>`].
+//!
+//! | method | self | function input | function result | output |
+//! |--------------|-----------|----------------|-----------------|-----------|
+//! | [`and_then`] | `None` | (not provided) | (not evaluated) | `None` |
+//! | [`and_then`] | `Some(x)` | `x` | `None` | `None` |
+//! | [`and_then`] | `Some(x)` | `x` | `Some(y)` | `Some(y)` |
+//! | [`or_else`] | `None` | (not provided) | `None` | `None` |
+//! | [`or_else`] | `None` | (not provided) | `Some(y)` | `Some(y)` |
+//! | [`or_else`] | `Some(x)` | (not provided) | (not evaluated) | `Some(x)` |
+//!
+//! [`and_then`]: Option::and_then
+//! [`or_else`]: Option::or_else
+//!
+//! This is an example of using methods like [`and_then`] and [`or`] in a
+//! pipeline of method calls. Early stages of the pipeline pass failure
+//! values ([`None`]) through unchanged, and continue processing on
+//! success values ([`Some`]). Toward the end, [`or`] substitutes an error
+//! message if it receives [`None`].
+//!
+//! ```
+//! # use std::collections::BTreeMap;
+//! let mut bt = BTreeMap::new();
+//! bt.insert(20u8, "foo");
+//! bt.insert(42u8, "bar");
+//! let res = [0u8, 1, 11, 200, 22]
+//! .into_iter()
+//! .map(|x| {
+//! // `checked_sub()` returns `None` on error
+//! x.checked_sub(1)
+//! // same with `checked_mul()`
+//! .and_then(|x| x.checked_mul(2))
+//! // `BTreeMap::get` returns `None` on error
+//! .and_then(|x| bt.get(&x))
+//! // Substitute an error message if we have `None` so far
+//! .or(Some(&"error!"))
+//! .copied()
+//! // Won't panic because we unconditionally used `Some` above
+//! .unwrap()
+//! })
+//! .collect::<Vec<_>>();
+//! assert_eq!(res, ["error!", "error!", "foo", "error!", "bar"]);
+//! ```
+//!
+//! ## Comparison operators
+//!
+//! If `T` implements [`PartialOrd`] then [`Option<T>`] will derive its
+//! [`PartialOrd`] implementation. With this order, [`None`] compares as
+//! less than any [`Some`], and two [`Some`] compare the same way as their
+//! contained values would in `T`. If `T` also implements
+//! [`Ord`], then so does [`Option<T>`].
+//!
+//! ```
+//! assert!(None < Some(0));
+//! assert!(Some(0) < Some(1));
+//! ```
+//!
+//! ## Iterating over `Option`
+//!
+//! An [`Option`] can be iterated over. This can be helpful if you need an
+//! iterator that is conditionally empty. The iterator will either produce
+//! a single value (when the [`Option`] is [`Some`]), or produce no values
+//! (when the [`Option`] is [`None`]). For example, [`into_iter`] acts like
+//! [`once(v)`] if the [`Option`] is [`Some(v)`], and like [`empty()`] if
+//! the [`Option`] is [`None`].
+//!
+//! [`Some(v)`]: Some
+//! [`empty()`]: crate::iter::empty
+//! [`once(v)`]: crate::iter::once
+//!
+//! Iterators over [`Option<T>`] come in three types:
+//!
+//! * [`into_iter`] consumes the [`Option`] and produces the contained
+//! value
+//! * [`iter`] produces an immutable reference of type `&T` to the
+//! contained value
+//! * [`iter_mut`] produces a mutable reference of type `&mut T` to the
+//! contained value
+//!
+//! [`into_iter`]: Option::into_iter
+//! [`iter`]: Option::iter
+//! [`iter_mut`]: Option::iter_mut
+//!
+//! An iterator over [`Option`] can be useful when chaining iterators, for
+//! example, to conditionally insert items. (It's not always necessary to
+//! explicitly call an iterator constructor: many [`Iterator`] methods that
+//! accept other iterators will also accept iterable types that implement
+//! [`IntoIterator`], which includes [`Option`].)
+//!
+//! ```
+//! let yep = Some(42);
+//! let nope = None;
+//! // chain() already calls into_iter(), so we don't have to do so
+//! let nums: Vec<i32> = (0..4).chain(yep).chain(4..8).collect();
+//! assert_eq!(nums, [0, 1, 2, 3, 42, 4, 5, 6, 7]);
+//! let nums: Vec<i32> = (0..4).chain(nope).chain(4..8).collect();
+//! assert_eq!(nums, [0, 1, 2, 3, 4, 5, 6, 7]);
+//! ```
+//!
+//! One reason to chain iterators in this way is that a function returning
+//! `impl Iterator` must have all possible return values be of the same
+//! concrete type. Chaining an iterated [`Option`] can help with that.
+//!
+//! ```
+//! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> {
+//! // Explicit returns to illustrate return types matching
+//! match do_insert {
+//! true => return (0..4).chain(Some(42)).chain(4..8),
+//! false => return (0..4).chain(None).chain(4..8),
+//! }
+//! }
+//! println!("{:?}", make_iter(true).collect::<Vec<_>>());
+//! println!("{:?}", make_iter(false).collect::<Vec<_>>());
+//! ```
+//!
+//! If we try to do the same thing, but using [`once()`] and [`empty()`],
+//! we can't return `impl Iterator` anymore because the concrete types of
+//! the return values differ.
+//!
+//! [`empty()`]: crate::iter::empty
+//! [`once()`]: crate::iter::once
+//!
+//! ```compile_fail,E0308
+//! # use std::iter::{empty, once};
+//! // This won't compile because all possible returns from the function
+//! // must have the same concrete type.
+//! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> {
+//! // Explicit returns to illustrate return types not matching
+//! match do_insert {
+//! true => return (0..4).chain(once(42)).chain(4..8),
+//! false => return (0..4).chain(empty()).chain(4..8),
+//! }
+//! }
+//! ```
+//!
+//! ## Collecting into `Option`
+//!
+//! [`Option`] implements the [`FromIterator`][impl-FromIterator] trait,
+//! which allows an iterator over [`Option`] values to be collected into an
+//! [`Option`] of a collection of each contained value of the original
+//! [`Option`] values, or [`None`] if any of the elements was [`None`].
+//!
+//! [impl-FromIterator]: Option#impl-FromIterator%3COption%3CA%3E%3E
+//!
+//! ```
+//! let v = [Some(2), Some(4), None, Some(8)];
+//! let res: Option<Vec<_>> = v.into_iter().collect();
+//! assert_eq!(res, None);
+//! let v = [Some(2), Some(4), Some(8)];
+//! let res: Option<Vec<_>> = v.into_iter().collect();
+//! assert_eq!(res, Some(vec![2, 4, 8]));
+//! ```
+//!
+//! [`Option`] also implements the [`Product`][impl-Product] and
+//! [`Sum`][impl-Sum] traits, allowing an iterator over [`Option`] values
+//! to provide the [`product`][Iterator::product] and
+//! [`sum`][Iterator::sum] methods.
+//!
+//! [impl-Product]: Option#impl-Product%3COption%3CU%3E%3E
+//! [impl-Sum]: Option#impl-Sum%3COption%3CU%3E%3E
+//!
+//! ```
+//! let v = [None, Some(1), Some(2), Some(3)];
+//! let res: Option<i32> = v.into_iter().sum();
+//! assert_eq!(res, None);
+//! let v = [Some(1), Some(2), Some(21)];
+//! let res: Option<i32> = v.into_iter().product();
+//! assert_eq!(res, Some(42));
+//! ```
+//!
+//! ## Modifying an [`Option`] in-place
+//!
+//! These methods return a mutable reference to the contained value of an
+//! [`Option<T>`]:
+//!
+//! * [`insert`] inserts a value, dropping any old contents
+//! * [`get_or_insert`] gets the current value, inserting a provided
+//! default value if it is [`None`]
+//! * [`get_or_insert_default`] gets the current value, inserting the
+//! default value of type `T` (which must implement [`Default`]) if it is
+//! [`None`]
+//! * [`get_or_insert_with`] gets the current value, inserting a default
+//! computed by the provided function if it is [`None`]
+//!
+//! [`get_or_insert`]: Option::get_or_insert
+//! [`get_or_insert_default`]: Option::get_or_insert_default
+//! [`get_or_insert_with`]: Option::get_or_insert_with
+//! [`insert`]: Option::insert
+//!
+//! These methods transfer ownership of the contained value of an
+//! [`Option`]:
+//!
+//! * [`take`] takes ownership of the contained value of an [`Option`], if
+//! any, replacing the [`Option`] with [`None`]
+//! * [`replace`] takes ownership of the contained value of an [`Option`],
+//! if any, replacing the [`Option`] with a [`Some`] containing the
+//! provided value
+//!
+//! [`replace`]: Option::replace
+//! [`take`]: Option::take
//!
//! # Examples
//!
//! }
//!
//! match name_of_biggest_animal {
-//! Some(name) => println!("the biggest animal is {}", name),
+//! Some(name) => println!("the biggest animal is {name}"),
//! None => println!("there are no animals :("),
//! }
//! ```
-//!
-//! [`Box<T>`]: ../../std/boxed/struct.Box.html
#![stable(feature = "rust1", since = "1.0.0")]
-use crate::iter::{FromIterator, FusedIterator, TrustedLen};
+use crate::iter::{self, FromIterator, FusedIterator, TrustedLen};
+use crate::marker::Destruct;
+use crate::panicking::{panic, panic_str};
use crate::pin::Pin;
use crate::{
- convert, fmt, hint, mem,
- ops::{self, Deref, DerefMut},
+ convert, hint, mem,
+ ops::{self, ControlFlow, Deref, DerefMut},
};
/// The `Option` type. See [the module level documentation](self) for more.
#[derive(Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
-#[rustc_diagnostic_item = "option_type"]
+#[rustc_diagnostic_item = "Option"]
#[stable(feature = "rust1", since = "1.0.0")]
pub enum Option<T> {
- /// No value
- #[cfg_attr(not(bootstrap), lang = "None")]
+ /// No value.
+ #[lang = "None"]
#[stable(feature = "rust1", since = "1.0.0")]
None,
- /// Some value `T`
- #[cfg_attr(not(bootstrap), lang = "Some")]
+ /// Some value of type `T`.
+ #[lang = "Some"]
#[stable(feature = "rust1", since = "1.0.0")]
Some(#[stable(feature = "rust1", since = "1.0.0")] T),
}
/// ```
#[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"]
#[inline]
- #[rustc_const_unstable(feature = "const_option", issue = "67441")]
#[stable(feature = "rust1", since = "1.0.0")]
+ #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
pub const fn is_some(&self) -> bool {
matches!(*self, Some(_))
}
- /// Returns `true` if the option is a [`None`] value.
+ /// Returns `true` if the option is a [`Some`] and the value inside of it matches a predicate.
///
/// # Examples
///
/// ```
+ /// #![feature(is_some_with)]
+ ///
/// let x: Option<u32> = Some(2);
- /// assert_eq!(x.is_none(), false);
+ /// assert_eq!(x.is_some_and(|&x| x > 1), true);
+ ///
+ /// let x: Option<u32> = Some(0);
+ /// assert_eq!(x.is_some_and(|&x| x > 1), false);
///
/// let x: Option<u32> = None;
- /// assert_eq!(x.is_none(), true);
+ /// assert_eq!(x.is_some_and(|&x| x > 1), false);
/// ```
- #[must_use = "if you intended to assert that this doesn't have a value, consider \
- `.and_then(|| panic!(\"`Option` had a value when expected `None`\"))` instead"]
+ #[must_use]
#[inline]
- #[rustc_const_unstable(feature = "const_option", issue = "67441")]
- #[stable(feature = "rust1", since = "1.0.0")]
- pub const fn is_none(&self) -> bool {
- !self.is_some()
+ #[unstable(feature = "is_some_with", issue = "93050")]
+ pub fn is_some_and(&self, f: impl FnOnce(&T) -> bool) -> bool {
+ matches!(self, Some(x) if f(x))
}
- /// Returns `true` if the option is a [`Some`] value containing the given value.
+ /// Returns `true` if the option is a [`None`] value.
///
/// # Examples
///
/// ```
- /// #![feature(option_result_contains)]
- ///
/// let x: Option<u32> = Some(2);
- /// assert_eq!(x.contains(&2), true);
- ///
- /// let x: Option<u32> = Some(3);
- /// assert_eq!(x.contains(&2), false);
+ /// assert_eq!(x.is_none(), false);
///
/// let x: Option<u32> = None;
- /// assert_eq!(x.contains(&2), false);
+ /// assert_eq!(x.is_none(), true);
/// ```
- #[must_use]
+ #[must_use = "if you intended to assert that this doesn't have a value, consider \
+ `.and_then(|_| panic!(\"`Option` had a value when expected `None`\"))` instead"]
#[inline]
- #[unstable(feature = "option_result_contains", issue = "62358")]
- pub fn contains<U>(&self, x: &U) -> bool
- where
- U: PartialEq<T>,
- {
- match self {
- Some(y) => x == y,
- None => false,
- }
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
+ pub const fn is_none(&self) -> bool {
+ !self.is_some()
}
/////////////////////////////////////////////////////////////////////////
///
/// # Examples
///
- /// Converts an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, preserving the original.
- /// The [`map`] method takes the `self` argument by value, consuming the original,
+ /// Converts an <code>Option<[String]></code> into an <code>Option<[usize]></code>, 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`]: Option::map
- /// [`String`]: ../../std/string/struct.String.html
+ /// [String]: ../../std/string/struct.String.html "String"
///
/// ```
/// let text: Option<String> = Some("Hello, world!".to_string());
/// // First, cast `Option<String>` to `Option<&String>` with `as_ref`,
/// // then consume *that* with `map`, leaving `text` on the stack.
/// let text_length: Option<usize> = text.as_ref().map(|s| s.len());
- /// println!("still can print text: {:?}", text);
+ /// println!("still can print text: {text:?}");
/// ```
#[inline]
- #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]
#[stable(feature = "rust1", since = "1.0.0")]
pub const fn as_ref(&self) -> Option<&T> {
match *self {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn as_mut(&mut self) -> Option<&mut T> {
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn as_mut(&mut self) -> Option<&mut T> {
match *self {
Some(ref mut x) => Some(x),
None => None,
}
}
- /// Converts from [`Pin`]`<&Option<T>>` to `Option<`[`Pin`]`<&T>>`.
+ /// Converts from <code>[Pin]<[&]Option\<T>></code> to <code>Option<[Pin]<[&]T>></code>.
+ ///
+ /// [&]: reference "shared reference"
#[inline]
+ #[must_use]
#[stable(feature = "pin", since = "1.33.0")]
- pub fn as_pin_ref(self: Pin<&Self>) -> Option<Pin<&T>> {
- // SAFETY: `x` is guaranteed to be pinned because it comes from `self`
- // which is pinned.
- unsafe { Pin::get_ref(self).as_ref().map(|x| Pin::new_unchecked(x)) }
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_pin_ref(self: Pin<&Self>) -> Option<Pin<&T>> {
+ match Pin::get_ref(self).as_ref() {
+ // SAFETY: `x` is guaranteed to be pinned because it comes from `self`
+ // which is pinned.
+ Some(x) => unsafe { Some(Pin::new_unchecked(x)) },
+ None => None,
+ }
}
- /// Converts from [`Pin`]`<&mut Option<T>>` to `Option<`[`Pin`]`<&mut T>>`.
+ /// Converts from <code>[Pin]<[&mut] Option\<T>></code> to <code>Option<[Pin]<[&mut] T>></code>.
+ ///
+ /// [&mut]: reference "mutable reference"
#[inline]
+ #[must_use]
#[stable(feature = "pin", since = "1.33.0")]
- pub fn as_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>> {
// SAFETY: `get_unchecked_mut` is never used to move the `Option` inside `self`.
// `x` is guaranteed to be pinned because it comes from `self` which is pinned.
- unsafe { Pin::get_unchecked_mut(self).as_mut().map(|x| Pin::new_unchecked(x)) }
+ unsafe {
+ match Pin::get_unchecked_mut(self).as_mut() {
+ Some(x) => Some(Pin::new_unchecked(x)),
+ None => None,
+ }
+ }
}
/////////////////////////////////////////////////////////////////////////
/// assert_eq!(x.expect("fruits are healthy"), "value");
/// ```
///
- /// ```{.should_panic}
+ /// ```should_panic
/// let x: Option<&str> = None;
/// x.expect("fruits are healthy"); // panics with `fruits are healthy`
/// ```
+ ///
+ /// # Recommended Message Style
+ ///
+ /// We recommend that `expect` messages are used to describe the reason you
+ /// _expect_ the `Option` should be `Some`.
+ ///
+ /// ```should_panic
+ /// # let slice: &[u8] = &[];
+ /// let item = slice.get(0)
+ /// .expect("slice should not be empty");
+ /// ```
+ ///
+ /// **Hint**: If you're having trouble remembering how to phrase expect
+ /// error messages remember to focus on the word "should" as in "env
+ /// variable should be set by blah" or "the given binary should be available
+ /// and executable by the current user".
+ ///
+ /// For more detail on expect message styles and the reasoning behind our
+ /// recommendation please refer to the section on ["Common Message
+ /// Styles"](../../std/error/index.html#common-message-styles) in the [`std::error`](../../std/error/index.html) module docs.
#[inline]
#[track_caller]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn expect(self, msg: &str) -> T {
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn expect(self, msg: &str) -> T {
match self {
Some(val) => val,
None => expect_failed(msg),
/// assert_eq!(x.unwrap(), "air");
/// ```
///
- /// ```{.should_panic}
+ /// ```should_panic
/// let x: Option<&str> = None;
/// assert_eq!(x.unwrap(), "air"); // fails
/// ```
pub const fn unwrap(self) -> T {
match self {
Some(val) => val,
- None => panic!("called `Option::unwrap()` on a `None` value"),
+ None => panic("called `Option::unwrap()` on a `None` value"),
}
}
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn unwrap_or(self, default: T) -> T {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn unwrap_or(self, default: T) -> T
+ where
+ T: ~const Destruct,
+ {
match self {
Some(x) => x,
None => default,
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn unwrap_or_else<F>(self, f: F) -> T
+ where
+ F: ~const FnOnce() -> T,
+ F: ~const Destruct,
+ {
match self {
Some(x) => x,
None => f(),
}
}
+ /// Returns the contained [`Some`] 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
+ ///
+ /// Converts 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);
+ /// ```
+ ///
+ /// [default value]: Default::default
+ /// [`parse`]: str::parse
+ /// [`FromStr`]: crate::str::FromStr
+ #[inline]
+ #[stable(feature = "rust1", since = "1.0.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn unwrap_or_default(self) -> T
+ where
+ T: ~const Default,
+ {
+ match self {
+ Some(x) => x,
+ None => Default::default(),
+ }
+ }
+
+ /// Returns the contained [`Some`] value, consuming the `self` value,
+ /// without checking that the value is not [`None`].
+ ///
+ /// # Safety
+ ///
+ /// Calling this method on [`None`] is *[undefined behavior]*.
+ ///
+ /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let x = Some("air");
+ /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air");
+ /// ```
+ ///
+ /// ```no_run
+ /// let x: Option<&str> = None;
+ /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
+ /// ```
+ #[inline]
+ #[track_caller]
+ #[stable(feature = "option_result_unwrap_unchecked", since = "1.58.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const unsafe fn unwrap_unchecked(self) -> T {
+ debug_assert!(self.is_some());
+ match self {
+ Some(val) => val,
+ // SAFETY: the safety contract must be upheld by the caller.
+ None => unsafe { hint::unreachable_unchecked() },
+ }
+ }
+
/////////////////////////////////////////////////////////////////////////
// Transforming contained values
/////////////////////////////////////////////////////////////////////////
///
/// # Examples
///
- /// Converts an `Option<`[`String`]`>` into an `Option<`[`usize`]`>`, consuming the original:
+ /// Converts an <code>Option<[String]></code> into an <code>Option<[usize]></code>, consuming
+ /// the original:
///
- /// [`String`]: ../../std/string/struct.String.html
+ /// [String]: ../../std/string/struct.String.html "String"
/// ```
/// let maybe_some_string = Some(String::from("Hello, World!"));
/// // `Option::map` takes self *by value*, consuming `maybe_some_string`
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn map<U, F>(self, f: F) -> Option<U>
+ where
+ F: ~const FnOnce(T) -> U,
+ F: ~const Destruct,
+ {
match self {
Some(x) => Some(f(x)),
None => None,
}
}
- /// Applies a function to the contained value (if any),
- /// or returns the provided default (if not).
+ /// Calls the provided closure with a reference to the contained value (if [`Some`]).
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(result_option_inspect)]
+ ///
+ /// let v = vec![1, 2, 3, 4, 5];
+ ///
+ /// // prints "got: 4"
+ /// let x: Option<&usize> = v.get(3).inspect(|x| println!("got: {x}"));
+ ///
+ /// // prints nothing
+ /// let x: Option<&usize> = v.get(5).inspect(|x| println!("got: {x}"));
+ /// ```
+ #[inline]
+ #[unstable(feature = "result_option_inspect", issue = "91345")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn inspect<F>(self, f: F) -> Self
+ where
+ F: ~const FnOnce(&T),
+ F: ~const Destruct,
+ {
+ if let Some(ref x) = self {
+ f(x);
+ }
+
+ self
+ }
+
+ /// Returns the provided default result (if none),
+ /// or applies a function to the contained value (if any).
///
/// Arguments passed to `map_or` are eagerly evaluated; if you are passing
/// the result of a function call, it is recommended to use [`map_or_else`],
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn map_or<U, F>(self, default: U, f: F) -> U
+ where
+ F: ~const FnOnce(T) -> U,
+ F: ~const Destruct,
+ U: ~const Destruct,
+ {
match self {
Some(t) => f(t),
None => default,
}
}
- /// Applies a function to the contained value (if any),
- /// or computes a default (if not).
+ /// Computes a default function result (if none), or
+ /// applies a different function to the contained value (if any).
///
/// # Examples
///
/// ```
#[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 {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn map_or_else<U, D, F>(self, default: D, f: F) -> U
+ where
+ D: ~const FnOnce() -> U,
+ D: ~const Destruct,
+ F: ~const FnOnce(T) -> U,
+ F: ~const Destruct,
+ {
match self {
Some(t) => f(t),
None => default(),
/// result of a function call, it is recommended to use [`ok_or_else`], which is
/// lazily evaluated.
///
- /// [`Result<T, E>`]: Result
/// [`Ok(v)`]: Ok
/// [`Err(err)`]: Err
/// [`Some(v)`]: Some
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn ok_or<E>(self, err: E) -> Result<T, E> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn ok_or<E>(self, err: E) -> Result<T, E>
+ where
+ E: ~const Destruct,
+ {
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())`].
///
- /// [`Result<T, E>`]: Result
/// [`Ok(v)`]: Ok
/// [`Err(err())`]: Err
/// [`Some(v)`]: Some
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn ok_or_else<E, F>(self, err: F) -> Result<T, E>
+ where
+ F: ~const FnOnce() -> E,
+ F: ~const Destruct,
+ {
match self {
Some(v) => Ok(v),
None => Err(err()),
}
}
+ /// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`.
+ ///
+ /// Leaves the original Option in-place, creating a new one with a reference
+ /// to the original one, additionally coercing the contents via [`Deref`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let x: Option<String> = Some("hey".to_owned());
+ /// assert_eq!(x.as_deref(), Some("hey"));
+ ///
+ /// let x: Option<String> = None;
+ /// assert_eq!(x.as_deref(), None);
+ /// ```
+ #[stable(feature = "option_deref", since = "1.40.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_deref(&self) -> Option<&T::Target>
+ where
+ T: ~const Deref,
+ {
+ match self.as_ref() {
+ Some(t) => Some(t.deref()),
+ None => None,
+ }
+ }
+
+ /// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`.
+ ///
+ /// Leaves the original `Option` in-place, creating a new one containing a mutable reference to
+ /// the inner type's [`Deref::Target`] type.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut x: Option<String> = Some("hey".to_owned());
+ /// assert_eq!(x.as_deref_mut().map(|x| {
+ /// x.make_ascii_uppercase();
+ /// x
+ /// }), Some("HEY".to_owned().as_mut_str()));
+ /// ```
+ #[stable(feature = "option_deref", since = "1.40.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn as_deref_mut(&mut self) -> Option<&mut T::Target>
+ where
+ T: ~const DerefMut,
+ {
+ match self.as_mut() {
+ Some(t) => Some(t.deref_mut()),
+ None => None,
+ }
+ }
+
/////////////////////////////////////////////////////////////////////////
// Iterator constructors
/////////////////////////////////////////////////////////////////////////
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn and<U>(self, optb: Option<U>) -> Option<U> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn and<U>(self, optb: Option<U>) -> Option<U>
+ where
+ T: ~const Destruct,
+ U: ~const Destruct,
+ {
match self {
Some(_) => optb,
None => None,
/// # Examples
///
/// ```
- /// fn sq(x: u32) -> Option<u32> { Some(x * x) }
- /// fn nope(_: u32) -> Option<u32> { None }
+ /// fn sq_then_to_string(x: u32) -> Option<String> {
+ /// x.checked_mul(x).map(|sq| sq.to_string())
+ /// }
+ ///
+ /// assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
+ /// assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
+ /// assert_eq!(None.and_then(sq_then_to_string), None);
+ /// ```
+ ///
+ /// Often used to chain fallible operations that may return [`None`].
+ ///
+ /// ```
+ /// let arr_2d = [["A0", "A1"], ["B0", "B1"]];
///
- /// 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);
+ /// let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
+ /// assert_eq!(item_0_1, Some(&"A1"));
+ ///
+ /// let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
+ /// assert_eq!(item_2_0, None);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn and_then<U, F: FnOnce(T) -> Option<U>>(self, f: F) -> Option<U> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn and_then<U, F>(self, f: F) -> Option<U>
+ where
+ F: ~const FnOnce(T) -> Option<U>,
+ F: ~const Destruct,
+ {
match self {
Some(x) => f(x),
None => None,
/// assert_eq!(Some(4).filter(is_even), Some(4));
/// ```
///
+ /// [`Some(t)`]: Some
#[inline]
#[stable(feature = "option_filter", since = "1.27.0")]
- pub fn filter<P: FnOnce(&T) -> bool>(self, predicate: P) -> Self {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn filter<P>(self, predicate: P) -> Self
+ where
+ T: ~const Destruct,
+ P: ~const FnOnce(&T) -> bool,
+ P: ~const Destruct,
+ {
if let Some(x) = self {
if predicate(&x) {
return Some(x);
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn or(self, optb: Option<T>) -> Option<T> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn or(self, optb: Option<T>) -> Option<T>
+ where
+ T: ~const Destruct,
+ {
match self {
- Some(_) => self,
+ Some(x) => Some(x),
None => optb,
}
}
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn or_else<F>(self, f: F) -> Option<T>
+ where
+ F: ~const FnOnce() -> Option<T>,
+ F: ~const Destruct,
+ {
match self {
- Some(_) => self,
+ Some(x) => Some(x),
None => f(),
}
}
/// let y = Some(2);
/// assert_eq!(x.xor(y), Some(2));
///
- /// let x = Some(2);
- /// let y = Some(2);
- /// assert_eq!(x.xor(y), None);
+ /// let x = Some(2);
+ /// let y = Some(2);
+ /// assert_eq!(x.xor(y), None);
+ ///
+ /// let x: Option<u32> = None;
+ /// let y: Option<u32> = None;
+ /// assert_eq!(x.xor(y), None);
+ /// ```
+ #[inline]
+ #[stable(feature = "option_xor", since = "1.37.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn xor(self, optb: Option<T>) -> Option<T>
+ where
+ T: ~const Destruct,
+ {
+ match (self, optb) {
+ (Some(a), None) => Some(a),
+ (None, Some(b)) => Some(b),
+ _ => None,
+ }
+ }
+
+ /////////////////////////////////////////////////////////////////////////
+ // Entry-like operations to insert a value and return a reference
+ /////////////////////////////////////////////////////////////////////////
+
+ /// Inserts `value` into the option, then returns a mutable reference to it.
+ ///
+ /// If the option already contains a value, the old value is dropped.
+ ///
+ /// See also [`Option::get_or_insert`], which doesn't update the value if
+ /// the option already contains [`Some`].
+ ///
+ /// # Example
+ ///
+ /// ```
+ /// let mut opt = None;
+ /// let val = opt.insert(1);
+ /// assert_eq!(*val, 1);
+ /// assert_eq!(opt.unwrap(), 1);
+ /// let val = opt.insert(2);
+ /// assert_eq!(*val, 2);
+ /// *val = 3;
+ /// assert_eq!(opt.unwrap(), 3);
+ /// ```
+ #[must_use = "if you intended to set a value, consider assignment instead"]
+ #[inline]
+ #[stable(feature = "option_insert", since = "1.53.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn insert(&mut self, value: T) -> &mut T
+ where
+ T: ~const Destruct,
+ {
+ *self = Some(value);
+
+ // SAFETY: the code above just filled the option
+ unsafe { self.as_mut().unwrap_unchecked() }
+ }
+
+ /// Inserts `value` into the option if it is [`None`], then
+ /// returns a mutable reference to the contained value.
+ ///
+ /// See also [`Option::insert`], which updates the value even if
+ /// the option already contains [`Some`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// let mut x = None;
+ ///
+ /// {
+ /// let y: &mut u32 = x.get_or_insert(5);
+ /// assert_eq!(y, &5);
///
- /// let x: Option<u32> = None;
- /// let y: Option<u32> = None;
- /// assert_eq!(x.xor(y), None);
+ /// *y = 7;
+ /// }
+ ///
+ /// assert_eq!(x, Some(7));
/// ```
#[inline]
- #[stable(feature = "option_xor", since = "1.37.0")]
- pub fn xor(self, optb: Option<T>) -> Option<T> {
- match (self, optb) {
- (Some(a), None) => Some(a),
- (None, Some(b)) => Some(b),
- _ => None,
+ #[stable(feature = "option_entry", since = "1.20.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn get_or_insert(&mut self, value: T) -> &mut T
+ where
+ T: ~const Destruct,
+ {
+ if let None = *self {
+ *self = Some(value);
}
- }
- /////////////////////////////////////////////////////////////////////////
- // Entry-like operations to insert if None and return a reference
- /////////////////////////////////////////////////////////////////////////
+ // SAFETY: a `None` variant for `self` would have been replaced by a `Some`
+ // variant in the code above.
+ unsafe { self.as_mut().unwrap_unchecked() }
+ }
- /// Inserts `v` into the option if it is [`None`], then
+ /// Inserts the default value into the option if it is [`None`], then
/// returns a mutable reference to the contained value.
///
/// # Examples
///
/// ```
+ /// #![feature(option_get_or_insert_default)]
+ ///
/// let mut x = None;
///
/// {
- /// let y: &mut u32 = x.get_or_insert(5);
- /// assert_eq!(y, &5);
+ /// let y: &mut u32 = x.get_or_insert_default();
+ /// assert_eq!(y, &0);
///
/// *y = 7;
/// }
/// assert_eq!(x, Some(7));
/// ```
#[inline]
- #[stable(feature = "option_entry", since = "1.20.0")]
- pub fn get_or_insert(&mut self, v: T) -> &mut T {
- self.get_or_insert_with(|| v)
+ #[unstable(feature = "option_get_or_insert_default", issue = "82901")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn get_or_insert_default(&mut self) -> &mut T
+ where
+ T: ~const Default,
+ {
+ const fn default<T: ~const Default>() -> T {
+ T::default()
+ }
+
+ self.get_or_insert_with(default)
}
- /// Inserts a value computed from `f` into the option if it is [`None`], then
- /// returns a mutable reference to the contained value.
+ /// Inserts a value computed from `f` into the option if it is [`None`],
+ /// then returns a mutable reference to the contained value.
///
/// # Examples
///
/// ```
#[inline]
#[stable(feature = "option_entry", since = "1.20.0")]
- pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
+ where
+ F: ~const FnOnce() -> T,
+ F: ~const Destruct,
+ {
if let None = *self {
- *self = Some(f());
+ // the compiler isn't smart enough to know that we are not dropping a `T`
+ // here and wants us to ensure `T` can be dropped at compile time.
+ mem::forget(mem::replace(self, Some(f())))
}
- match *self {
- Some(ref mut v) => v,
- // SAFETY: a `None` variant for `self` would have been replaced by a `Some`
- // variant in the code above.
- None => unsafe { hint::unreachable_unchecked() },
- }
+ // SAFETY: a `None` variant for `self` would have been replaced by a `Some`
+ // variant in the code above.
+ unsafe { self.as_mut().unwrap_unchecked() }
}
/////////////////////////////////////////////////////////////////////////
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn take(&mut self) -> Option<T> {
- mem::take(self)
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn take(&mut self) -> Option<T> {
+ // FIXME replace `mem::replace` by `mem::take` when the latter is const ready
+ mem::replace(self, None)
}
/// Replaces the actual value in the option by the value given in parameter,
/// assert_eq!(old, None);
/// ```
#[inline]
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
#[stable(feature = "option_replace", since = "1.31.0")]
- pub fn replace(&mut self, value: T) -> Option<T> {
+ pub const fn replace(&mut self, value: T) -> Option<T> {
mem::replace(self, Some(value))
}
+ /// Returns `true` if the option is a [`Some`] value containing the given value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(option_result_contains)]
+ ///
+ /// let x: Option<u32> = Some(2);
+ /// assert_eq!(x.contains(&2), true);
+ ///
+ /// let x: Option<u32> = Some(3);
+ /// assert_eq!(x.contains(&2), false);
+ ///
+ /// let x: Option<u32> = None;
+ /// assert_eq!(x.contains(&2), false);
+ /// ```
+ #[must_use]
+ #[inline]
+ #[unstable(feature = "option_result_contains", issue = "62358")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn contains<U>(&self, x: &U) -> bool
+ where
+ U: ~const PartialEq<T>,
+ {
+ match self {
+ Some(y) => x.eq(y),
+ None => false,
+ }
+ }
+
/// Zips `self` with another `Option`.
///
/// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some((s, o))`.
/// assert_eq!(x.zip(z), None);
/// ```
#[stable(feature = "option_zip_option", since = "1.46.0")]
- pub fn zip<U>(self, other: Option<U>) -> Option<(T, U)> {
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn zip<U>(self, other: Option<U>) -> Option<(T, U)>
+ where
+ T: ~const Destruct,
+ U: ~const Destruct,
+ {
match (self, other) {
(Some(a), Some(b)) => Some((a, b)),
_ => None,
/// assert_eq!(x.zip_with(None, Point::new), None);
/// ```
#[unstable(feature = "option_zip", issue = "70086")]
- pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>
where
- F: FnOnce(T, U) -> R,
+ F: ~const FnOnce(T, U) -> R,
+ F: ~const Destruct,
+ T: ~const Destruct,
+ U: ~const Destruct,
{
- Some(f(self?, other?))
+ match (self, other) {
+ (Some(a), Some(b)) => Some(f(a, b)),
+ _ => None,
+ }
}
}
-impl<T: Copy> Option<&T> {
- /// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the
- /// option.
+impl<T, U> Option<(T, U)> {
+ /// Unzips an option containing a tuple of two options.
+ ///
+ /// If `self` is `Some((a, b))` this method returns `(Some(a), Some(b))`.
+ /// Otherwise, `(None, None)` is returned.
///
/// # Examples
///
/// ```
- /// let x = 12;
- /// let opt_x = Some(&x);
- /// assert_eq!(opt_x, Some(&12));
- /// let copied = opt_x.copied();
- /// assert_eq!(copied, Some(12));
+ /// #![feature(unzip_option)]
+ ///
+ /// let x = Some((1, "hi"));
+ /// let y = None::<(u8, u32)>;
+ ///
+ /// assert_eq!(x.unzip(), (Some(1), Some("hi")));
+ /// assert_eq!(y.unzip(), (None, None));
/// ```
- #[stable(feature = "copied", since = "1.35.0")]
- pub fn copied(self) -> Option<T> {
- self.map(|&t| t)
+ #[inline]
+ #[unstable(feature = "unzip_option", issue = "87800", reason = "recently added")]
+ pub const fn unzip(self) -> (Option<T>, Option<U>) {
+ match self {
+ Some((a, b)) => (Some(a), Some(b)),
+ None => (None, None),
+ }
}
}
-impl<T: Copy> Option<&mut T> {
- /// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the
+impl<T> Option<&T> {
+ /// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the
/// option.
///
/// # Examples
///
/// ```
- /// let mut x = 12;
- /// let opt_x = Some(&mut x);
- /// assert_eq!(opt_x, Some(&mut 12));
+ /// let x = 12;
+ /// let opt_x = Some(&x);
+ /// assert_eq!(opt_x, Some(&12));
/// let copied = opt_x.copied();
/// assert_eq!(copied, Some(12));
/// ```
+ #[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "copied", since = "1.35.0")]
- pub fn copied(self) -> Option<T> {
- self.map(|&mut t| t)
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn copied(self) -> Option<T>
+ where
+ T: Copy,
+ {
+ // FIXME: this implementation, which sidesteps using `Option::map` since it's not const
+ // ready yet, should be reverted when possible to avoid code repetition
+ match self {
+ Some(&v) => Some(v),
+ None => None,
+ }
}
-}
-impl<T: Clone> Option<&T> {
/// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the
/// option.
///
/// let cloned = opt_x.cloned();
/// assert_eq!(cloned, Some(12));
/// ```
+ #[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
- pub fn cloned(self) -> Option<T> {
- self.map(|t| t.clone())
+ #[rustc_const_unstable(feature = "const_option_cloned", issue = "91582")]
+ pub const fn cloned(self) -> Option<T>
+ where
+ T: ~const Clone,
+ {
+ match self {
+ Some(t) => Some(t.clone()),
+ None => None,
+ }
}
}
-impl<T: Clone> Option<&mut T> {
- /// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the
+impl<T> Option<&mut T> {
+ /// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the
/// option.
///
/// # Examples
/// let mut x = 12;
/// let opt_x = Some(&mut x);
/// assert_eq!(opt_x, Some(&mut 12));
- /// let cloned = opt_x.cloned();
- /// assert_eq!(cloned, Some(12));
- /// ```
- #[stable(since = "1.26.0", feature = "option_ref_mut_cloned")]
- pub fn cloned(self) -> Option<T> {
- self.map(|t| t.clone())
- }
-}
-
-impl<T: fmt::Debug> Option<T> {
- /// Consumes `self` while expecting [`None`] and returning nothing.
- ///
- /// # Panics
- ///
- /// Panics if the value is a [`Some`], with a panic message including the
- /// passed message, and the content of the [`Some`].
- ///
- /// # Examples
- ///
- /// ```
- /// #![feature(option_expect_none)]
- ///
- /// use std::collections::HashMap;
- /// let mut squares = HashMap::new();
- /// for i in -10..=10 {
- /// // This will not panic, since all keys are unique.
- /// squares.insert(i, i * i).expect_none("duplicate key");
- /// }
- /// ```
- ///
- /// ```{.should_panic}
- /// #![feature(option_expect_none)]
- ///
- /// use std::collections::HashMap;
- /// let mut sqrts = HashMap::new();
- /// for i in -10..=10 {
- /// // This will panic, since both negative and positive `i` will
- /// // insert the same `i * i` key, returning the old `Some(i)`.
- /// sqrts.insert(i * i, i).expect_none("duplicate key");
- /// }
- /// ```
- #[inline]
- #[track_caller]
- #[unstable(feature = "option_expect_none", reason = "newly added", issue = "62633")]
- pub fn expect_none(self, msg: &str) {
- if let Some(val) = self {
- expect_none_failed(msg, &val);
- }
- }
-
- /// Consumes `self` while expecting [`None`] and returning nothing.
- ///
- /// # Panics
- ///
- /// Panics if the value is a [`Some`], with a custom panic message provided
- /// by the [`Some`]'s value.
- ///
- /// [`Some(v)`]: Some
- ///
- /// # Examples
- ///
- /// ```
- /// #![feature(option_unwrap_none)]
- ///
- /// use std::collections::HashMap;
- /// let mut squares = HashMap::new();
- /// for i in -10..=10 {
- /// // This will not panic, since all keys are unique.
- /// squares.insert(i, i * i).unwrap_none();
- /// }
- /// ```
- ///
- /// ```{.should_panic}
- /// #![feature(option_unwrap_none)]
- ///
- /// use std::collections::HashMap;
- /// let mut sqrts = HashMap::new();
- /// for i in -10..=10 {
- /// // This will panic, since both negative and positive `i` will
- /// // insert the same `i * i` key, returning the old `Some(i)`.
- /// sqrts.insert(i * i, i).unwrap_none();
- /// }
+ /// let copied = opt_x.copied();
+ /// assert_eq!(copied, Some(12));
/// ```
- #[inline]
- #[track_caller]
- #[unstable(feature = "option_unwrap_none", reason = "newly added", issue = "62633")]
- pub fn unwrap_none(self) {
- if let Some(val) = self {
- expect_none_failed("called `Option::unwrap_none()` on a `Some` value", &val);
+ #[must_use = "`self` will be dropped if the result is not used"]
+ #[stable(feature = "copied", since = "1.35.0")]
+ #[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+ pub const fn copied(self) -> Option<T>
+ where
+ T: Copy,
+ {
+ match self {
+ Some(&mut t) => Some(t),
+ None => None,
}
}
-}
-impl<T: Default> Option<T> {
- /// Returns the contained [`Some`] 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.
+ /// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the
+ /// option.
///
/// # Examples
///
- /// Converts 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);
+ /// let mut x = 12;
+ /// let opt_x = Some(&mut x);
+ /// assert_eq!(opt_x, Some(&mut 12));
+ /// let cloned = opt_x.cloned();
+ /// assert_eq!(cloned, Some(12));
/// ```
- ///
- /// [default value]: Default::default
- /// [`parse`]: str::parse
- /// [`FromStr`]: crate::str::FromStr
- #[inline]
- #[stable(feature = "rust1", since = "1.0.0")]
- pub fn unwrap_or_default(self) -> T {
+ #[must_use = "`self` will be dropped if the result is not used"]
+ #[stable(since = "1.26.0", feature = "option_ref_mut_cloned")]
+ #[rustc_const_unstable(feature = "const_option_cloned", issue = "91582")]
+ pub const fn cloned(self) -> Option<T>
+ where
+ T: ~const Clone,
+ {
match self {
- Some(x) => x,
- None => Default::default(),
+ Some(t) => Some(t.clone()),
+ None => None,
}
}
}
-impl<T: Deref> Option<T> {
- /// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`.
- ///
- /// Leaves the original Option in-place, creating a new one with a reference
- /// to the original one, additionally coercing the contents via [`Deref`].
- ///
- /// # Examples
- ///
- /// ```
- /// let x: Option<String> = Some("hey".to_owned());
- /// assert_eq!(x.as_deref(), Some("hey"));
- ///
- /// let x: Option<String> = None;
- /// assert_eq!(x.as_deref(), None);
- /// ```
- #[stable(feature = "option_deref", since = "1.40.0")]
- pub fn as_deref(&self) -> Option<&T::Target> {
- self.as_ref().map(|t| t.deref())
- }
-}
-
-impl<T: DerefMut> Option<T> {
- /// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`.
- ///
- /// Leaves the original `Option` in-place, creating a new one containing a mutable reference to
- /// the inner type's `Deref::Target` type.
- ///
- /// # Examples
- ///
- /// ```
- /// let mut x: Option<String> = Some("hey".to_owned());
- /// assert_eq!(x.as_deref_mut().map(|x| {
- /// x.make_ascii_uppercase();
- /// x
- /// }), Some("HEY".to_owned().as_mut_str()));
- /// ```
- #[stable(feature = "option_deref", since = "1.40.0")]
- pub fn as_deref_mut(&mut self) -> Option<&mut T::Target> {
- self.as_mut().map(|t| t.deref_mut())
- }
-}
-
impl<T, E> Option<Result<T, E>> {
/// Transposes an `Option` of a [`Result`] into a [`Result`] of an `Option`.
///
- /// [`None`] will be mapped to [`Ok`]`(`[`None`]`)`.
- /// [`Some`]`(`[`Ok`]`(_))` and [`Some`]`(`[`Err`]`(_))` will be mapped to
- /// [`Ok`]`(`[`Some`]`(_))` and [`Err`]`(_)`.
+ /// [`None`] will be mapped to <code>[Ok]\([None])</code>.
+ /// <code>[Some]\([Ok]\(\_))</code> and <code>[Some]\([Err]\(\_))</code> will be mapped to
+ /// <code>[Ok]\([Some]\(\_))</code> and <code>[Err]\(\_)</code>.
///
/// # Examples
///
/// ```
#[inline]
#[stable(feature = "transpose_result", since = "1.33.0")]
- pub fn transpose(self) -> Result<Option<T>, E> {
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn transpose(self) -> Result<Option<T>, E> {
match self {
Some(Ok(x)) => Ok(Some(x)),
Some(Err(e)) => Err(e),
}
// This is a separate function to reduce the code size of .expect() itself.
-#[inline(never)]
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[cold]
#[track_caller]
-fn expect_failed(msg: &str) -> ! {
- panic!("{}", msg)
-}
-
-// This is a separate function to reduce the code size of .expect_none() itself.
-#[inline(never)]
-#[cold]
-#[track_caller]
-fn expect_none_failed(msg: &str, value: &dyn fmt::Debug) -> ! {
- panic!("{}: {:?}", msg, value)
+#[rustc_const_unstable(feature = "const_option", issue = "67441")]
+const fn expect_failed(msg: &str) -> ! {
+ panic_str(msg)
}
/////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////////
#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Clone> Clone for Option<T> {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl<T> const Clone for Option<T>
+where
+ T: ~const Clone + ~const Destruct,
+{
#[inline]
fn clone(&self) -> Self {
match self {
}
#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for Option<T> {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for Option<T> {
/// Returns [`None`][Option::None].
///
/// # Examples
}
#[stable(since = "1.12.0", feature = "option_from")]
-impl<T> From<T> for Option<T> {
- /// Copies `val` into a new `Some`.
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<T> const From<T> for Option<T> {
+ /// Moves `val` into a new [`Some`].
///
/// # Examples
///
}
#[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
-impl<'a, T> From<&'a Option<T>> for Option<&'a T> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<'a, T> const From<&'a Option<T>> for Option<&'a T> {
/// Converts from `&Option<T>` to `Option<&T>`.
///
/// # Examples
///
- /// Converts 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
+ /// Converts an <code>[Option]<[String]></code> into an <code>[Option]<[usize]></code>, preserving
+ /// the original. The [`map`] method takes the `self` argument by value, consuming the original,
+ /// so this technique uses `from` to first take an [`Option`] to a reference
/// to the value inside the original.
///
/// [`map`]: Option::map
- /// [`String`]: ../../std/string/struct.String.html
+ /// [String]: ../../std/string/struct.String.html "String"
///
/// ```
/// let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
/// let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());
///
- /// println!("Can still print s: {:?}", s);
+ /// println!("Can still print s: {s:?}");
///
/// assert_eq!(o, Some(18));
/// ```
}
#[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
-impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<'a, T> const From<&'a mut Option<T>> for Option<&'a mut T> {
/// Converts from `&mut Option<T>` to `Option<&mut T>`
///
/// # Examples
/// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none.
///
/// This `struct` is created by the [`Option::into_iter`] function.
-///
-/// [`Option::into_iter`]: enum.Option.html#method.into_iter
#[derive(Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct IntoIter<A> {
impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> {
/// Takes each element in the [`Iterator`]: if it is [`None`][Option::None],
/// no further elements are taken, and the [`None`][Option::None] is
- /// returned. Should no [`None`][Option::None] occur, a container with the
- /// values of each [`Option`] is returned.
+ /// returned. Should no [`None`][Option::None] occur, a container of type
+ /// `V` containing the values of each [`Option`] is returned.
///
/// # Examples
///
// FIXME(#11084): This could be replaced with Iterator::scan when this
// performance bug is closed.
- iter.into_iter().map(|x| x.ok_or(())).collect::<Result<_, _>>().ok()
+ iter::try_process(iter.into_iter(), |i| i.collect())
}
}
-/// The error type that results from applying the try operator (`?`) to a `None` value. If you wish
-/// to allow `x?` (where `x` is an `Option<T>`) to be converted into your error type, you can
-/// implement `impl From<NoneError>` for `YourErrorType`. In that case, `x?` within a function that
-/// returns `Result<_, YourErrorType>` will translate a `None` value into an `Err` result.
-#[rustc_diagnostic_item = "none_error"]
-#[unstable(feature = "try_trait", issue = "42327")]
-#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
-pub struct NoneError;
+#[unstable(feature = "try_trait_v2", issue = "84277")]
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<T> const ops::Try for Option<T> {
+ type Output = T;
+ type Residual = Option<convert::Infallible>;
-#[unstable(feature = "try_trait", issue = "42327")]
-impl<T> ops::Try for Option<T> {
- type Ok = T;
- type Error = NoneError;
+ #[inline]
+ fn from_output(output: Self::Output) -> Self {
+ Some(output)
+ }
#[inline]
- fn into_result(self) -> Result<T, NoneError> {
- self.ok_or(NoneError)
+ fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
+ match self {
+ Some(v) => ControlFlow::Continue(v),
+ None => ControlFlow::Break(None),
+ }
}
+}
+#[unstable(feature = "try_trait_v2", issue = "84277")]
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<T> const ops::FromResidual for Option<T> {
#[inline]
- fn from_ok(v: T) -> Self {
- Some(v)
+ fn from_residual(residual: Option<convert::Infallible>) -> Self {
+ match residual {
+ None => None,
+ }
}
+}
+#[unstable(feature = "try_trait_v2_yeet", issue = "96374")]
+impl<T> ops::FromResidual<ops::Yeet<()>> for Option<T> {
#[inline]
- fn from_error(_: NoneError) -> Self {
+ fn from_residual(ops::Yeet(()): ops::Yeet<()>) -> Self {
None
}
}
+#[unstable(feature = "try_trait_v2_residual", issue = "91285")]
+impl<T> ops::Residual<T> for Option<convert::Infallible> {
+ type TryType = Option<T>;
+}
+
impl<T> Option<Option<T>> {
- /// Converts from `Option<Option<T>>` to `Option<T>`
+ /// Converts from `Option<Option<T>>` to `Option<T>`.
///
/// # Examples
+ ///
/// Basic usage:
+ ///
/// ```
/// let x: Option<Option<u32>> = Some(Some(6));
/// assert_eq!(Some(6), x.flatten());
/// let x: Option<Option<u32>> = None;
/// assert_eq!(None, x.flatten());
/// ```
- /// Flattening once only removes one level of nesting:
+ ///
+ /// Flattening only removes one level of nesting at a time:
+ ///
/// ```
/// let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
/// assert_eq!(Some(Some(6)), x.flatten());
/// ```
#[inline]
#[stable(feature = "option_flattening", since = "1.40.0")]
- pub fn flatten(self) -> Option<T> {
- self.and_then(convert::identity)
+ #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+ pub const fn flatten(self) -> Option<T> {
+ match self {
+ Some(inner) => inner,
+ None => None,
+ }
}
}
projects / rustc.git / blobdiff