+++ /dev/null
-//! Traits for conversions between types.
-//!
-//! The traits in this module provide a way to convert from one type to another type.
-//! Each trait serves a different purpose:
-//!
-//! - Implement the [`AsRef`] trait for cheap reference-to-reference conversions
-//! - Implement the [`AsMut`] trait for cheap mutable-to-mutable conversions
-//! - Implement the [`From`] trait for consuming value-to-value conversions
-//! - Implement the [`Into`] trait for consuming value-to-value conversions to types
-//! outside the current crate
-//! - The [`TryFrom`] and [`TryInto`] traits behave like [`From`] and [`Into`],
-//! but should be implemented when the conversion can fail.
-//!
-//! The traits in this module are often used as trait bounds for generic functions such that to
-//! arguments of multiple types are supported. See the documentation of each trait for examples.
-//!
-//! As a library author, you should always prefer implementing [`From<T>`][`From`] or
-//! [`TryFrom<T>`][`TryFrom`] rather than [`Into<U>`][`Into`] or [`TryInto<U>`][`TryInto`],
-//! as [`From`] and [`TryFrom`] provide greater flexibility and offer
-//! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a
-//! blanket implementation in the standard library. Only implement [`Into`] or [`TryInto`]
-//! when a conversion to a type outside the current crate is required.
-//!
-//! # Generic Implementations
-//!
-//! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference
-//! - [`From`]`<U> for T` implies [`Into`]`<T> for U`
-//! - [`TryFrom`]`<U> for T` implies [`TryInto`]`<T> for U`
-//! - [`From`] and [`Into`] are reflexive, which means that all types can
-//! `into` themselves and `from` themselves
-//!
-//! See each trait for usage examples.
-//!
-//! [`Into`]: trait.Into.html
-//! [`From`]: trait.From.html
-//! [`TryFrom`]: trait.TryFrom.html
-//! [`TryInto`]: trait.TryInto.html
-//! [`AsRef`]: trait.AsRef.html
-//! [`AsMut`]: trait.AsMut.html
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-/// The identity function.
-///
-/// Two things are important to note about this function:
-///
-/// - It is not always equivalent to a closure like `|x| x`, since the
-/// closure may coerce `x` into a different type.
-///
-/// - It moves the input `x` passed to the function.
-///
-/// While it might seem strange to have a function that just returns back the
-/// input, there are some interesting uses.
-///
-/// # Examples
-///
-/// Using `identity` to do nothing in a sequence of other, interesting,
-/// functions:
-///
-/// ```rust
-/// use std::convert::identity;
-///
-/// fn manipulation(x: u32) -> u32 {
-/// // Let's pretend that adding one is an interesting function.
-/// x + 1
-/// }
-///
-/// let _arr = &[identity, manipulation];
-/// ```
-///
-/// Using `identity` as a "do nothing" base case in a conditional:
-///
-/// ```rust
-/// use std::convert::identity;
-///
-/// # let condition = true;
-/// #
-/// # fn manipulation(x: u32) -> u32 { x + 1 }
-/// #
-/// let do_stuff = if condition { manipulation } else { identity };
-///
-/// // Do more interesting stuff...
-///
-/// let _results = do_stuff(42);
-/// ```
-///
-/// Using `identity` to keep the `Some` variants of an iterator of `Option<T>`:
-///
-/// ```rust
-/// use std::convert::identity;
-///
-/// let iter = vec![Some(1), None, Some(3)].into_iter();
-/// let filtered = iter.filter_map(identity).collect::<Vec<_>>();
-/// assert_eq!(vec![1, 3], filtered);
-/// ```
-#[stable(feature = "convert_id", since = "1.33.0")]
-#[inline]
-pub const fn identity<T>(x: T) -> T {
- x
-}
-
-/// Used to do a cheap reference-to-reference conversion.
-///
-/// This trait is similar to [`AsMut`] which is used for converting between mutable references.
-/// If you need to do a costly conversion it is better to implement [`From`] with type
-/// `&T` or write a custom function.
-///
-/// `AsRef` has the same signature as [`Borrow`], but [`Borrow`] is different in few aspects:
-///
-/// - Unlike `AsRef`, [`Borrow`] has a blanket impl for any `T`, and can be used to accept either
-/// a reference or a value.
-/// - [`Borrow`] also requires that [`Hash`], [`Eq`] and [`Ord`] for borrowed value are
-/// equivalent to those of the owned value. For this reason, if you want to
-/// borrow only a single field of a struct you can implement `AsRef`, but not [`Borrow`].
-///
-/// **Note: This trait must not fail**. If the conversion can fail, use a
-/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
-///
-/// # Generic Implementations
-///
-/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
-/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type
-/// `&mut Foo` or `&&mut Foo`)
-///
-/// # Examples
-///
-/// By using trait bounds we can accept arguments of different types as long as they can be
-/// converted to the specified type `T`.
-///
-/// For example: By creating a generic function that takes an `AsRef<str>` we express that we
-/// want to accept all references that can be converted to [`&str`] as an argument.
-/// Since both [`String`] and [`&str`] implement `AsRef<str>` we can accept both as input argument.
-///
-/// [`Option<T>`]: ../../std/option/enum.Option.html
-/// [`Result<T, E>`]: ../../std/result/enum.Result.html
-/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
-/// [`Hash`]: ../../std/hash/trait.Hash.html
-/// [`Eq`]: ../../std/cmp/trait.Eq.html
-/// [`Ord`]: ../../std/cmp/trait.Ord.html
-/// [`&str`]: ../../std/primitive.str.html
-/// [`String`]: ../../std/string/struct.String.html
-///
-/// ```
-/// fn is_hello<T: AsRef<str>>(s: T) {
-/// assert_eq!("hello", s.as_ref());
-/// }
-///
-/// let s = "hello";
-/// is_hello(s);
-///
-/// let s = "hello".to_string();
-/// is_hello(s);
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait AsRef<T: ?Sized> {
- /// Performs the conversion.
- #[stable(feature = "rust1", since = "1.0.0")]
- fn as_ref(&self) -> &T;
-}
-
-/// Used to do a cheap mutable-to-mutable reference conversion.
-///
-/// This trait is similar to [`AsRef`] but used for converting between mutable
-/// references. If you need to do a costly conversion it is better to
-/// implement [`From`] with type `&mut T` or write a custom function.
-///
-/// **Note: This trait must not fail**. If the conversion can fail, use a
-/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
-///
-/// [`Option<T>`]: ../../std/option/enum.Option.html
-/// [`Result<T, E>`]: ../../std/result/enum.Result.html
-///
-/// # Generic Implementations
-///
-/// - `AsMut` auto-dereferences if the inner type is a mutable reference
-/// (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo`
-/// or `&mut &mut Foo`)
-///
-/// # Examples
-///
-/// Using `AsMut` as trait bound for a generic function we can accept all mutable references
-/// that can be converted to type `&mut T`. Because [`Box<T>`] implements `AsMut<T>` we can
-/// write a function `add_one` that takes all arguments that can be converted to `&mut u64`.
-/// Because [`Box<T>`] implements `AsMut<T>`, `add_one` accepts arguments of type
-/// `&mut Box<u64>` as well:
-///
-/// ```
-/// fn add_one<T: AsMut<u64>>(num: &mut T) {
-/// *num.as_mut() += 1;
-/// }
-///
-/// let mut boxed_num = Box::new(0);
-/// add_one(&mut boxed_num);
-/// assert_eq!(*boxed_num, 1);
-/// ```
-///
-/// [`Box<T>`]: ../../std/boxed/struct.Box.html
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait AsMut<T: ?Sized> {
- /// Performs the conversion.
- #[stable(feature = "rust1", since = "1.0.0")]
- fn as_mut(&mut self) -> &mut T;
-}
-
-/// A value-to-value conversion that consumes the input value. The
-/// opposite of [`From`].
-///
-/// One should avoid implementing [`Into`] and implement [`From`] instead.
-/// Implementing [`From`] automatically provides one with an implementation of [`Into`]
-/// thanks to the blanket implementation in the standard library.
-///
-/// Prefer using [`Into`] over [`From`] when specifying trait bounds on a generic function
-/// to ensure that types that only implement [`Into`] can be used as well.
-///
-/// **Note: This trait must not fail**. If the conversion can fail, use [`TryInto`].
-///
-/// # Generic Implementations
-///
-/// - [`From`]`<T> for U` implies `Into<U> for T`
-/// - [`Into`] is reflexive, which means that `Into<T> for T` is implemented
-///
-/// # Implementing [`Into`] for conversions to external types in old versions of Rust
-///
-/// Prior to Rust 1.40, if the destination type was not part of the current crate
-/// then you couldn't implement [`From`] directly.
-/// For example, take this code:
-///
-/// ```
-/// struct Wrapper<T>(Vec<T>);
-/// impl<T> From<Wrapper<T>> for Vec<T> {
-/// fn from(w: Wrapper<T>) -> Vec<T> {
-/// w.0
-/// }
-/// }
-/// ```
-/// This will fail to compile in older versions of the language because Rust's orphaning rules
-/// used to be a little bit more strict. To bypass this, you could implement [`Into`] directly:
-///
-/// ```
-/// struct Wrapper<T>(Vec<T>);
-/// impl<T> Into<Vec<T>> for Wrapper<T> {
-/// fn into(self) -> Vec<T> {
-/// self.0
-/// }
-/// }
-/// ```
-///
-/// It is important to understand that [`Into`] does not provide a [`From`] implementation
-/// (as [`From`] does with [`Into`]). Therefore, you should always try to implement [`From`]
-/// and then fall back to [`Into`] if [`From`] can't be implemented.
-///
-/// # Examples
-///
-/// [`String`] implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>`:
-///
-/// In order to express that we want a generic function to take all arguments that can be
-/// converted to a specified type `T`, we can use a trait bound of [`Into`]`<T>`.
-/// For example: The function `is_hello` takes all arguments that can be converted into a
-/// [`Vec`]`<`[`u8`]`>`.
-///
-/// ```
-/// fn is_hello<T: Into<Vec<u8>>>(s: T) {
-/// let bytes = b"hello".to_vec();
-/// assert_eq!(bytes, s.into());
-/// }
-///
-/// let s = "hello".to_string();
-/// is_hello(s);
-/// ```
-///
-/// [`TryInto`]: trait.TryInto.html
-/// [`Option<T>`]: ../../std/option/enum.Option.html
-/// [`Result<T, E>`]: ../../std/result/enum.Result.html
-/// [`String`]: ../../std/string/struct.String.html
-/// [`From`]: trait.From.html
-/// [`Into`]: trait.Into.html
-/// [`Vec`]: ../../std/vec/struct.Vec.html
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait Into<T>: Sized {
- /// Performs the conversion.
- #[stable(feature = "rust1", since = "1.0.0")]
- fn into(self) -> T;
-}
-
-/// Used to do value-to-value conversions while consuming the input value. It is the reciprocal of
-/// [`Into`].
-///
-/// One should always prefer implementing `From` over [`Into`]
-/// because implementing `From` automatically provides one with a implementation of [`Into`]
-/// thanks to the blanket implementation in the standard library.
-///
-/// Only implement [`Into`] if a conversion to a type outside the current crate is required.
-/// `From` cannot do these type of conversions because of Rust's orphaning rules.
-/// See [`Into`] for more details.
-///
-/// Prefer using [`Into`] over using `From` when specifying trait bounds on a generic function.
-/// This way, types that directly implement [`Into`] can be used as arguments as well.
-///
-/// The `From` is also very useful when performing error handling. When constructing a function
-/// that is capable of failing, the return type will generally be of the form `Result<T, E>`.
-/// The `From` trait simplifies error handling by allowing a function to return a single error type
-/// that encapsulate multiple error types. See the "Examples" section and [the book][book] for more
-/// details.
-///
-/// **Note: This trait must not fail**. If the conversion can fail, use [`TryFrom`].
-///
-/// # Generic Implementations
-///
-/// - `From<T> for U` implies [`Into`]`<U> for T`
-/// - `From` is reflexive, which means that `From<T> for T` is implemented
-///
-/// # Examples
-///
-/// [`String`] implements `From<&str>`:
-///
-/// An explicit conversion from a `&str` to a String is done as follows:
-///
-/// ```
-/// let string = "hello".to_string();
-/// let other_string = String::from("hello");
-///
-/// assert_eq!(string, other_string);
-/// ```
-///
-/// While performing error handling it is often useful to implement `From` for your own error type.
-/// By converting underlying error types to our own custom error type that encapsulates the
-/// underlying error type, we can return a single error type without losing information on the
-/// underlying cause. The '?' operator automatically converts the underlying error type to our
-/// custom error type by calling `Into<CliError>::into` which is automatically provided when
-/// implementing `From`. The compiler then infers which implementation of `Into` should be used.
-///
-/// ```
-/// use std::fs;
-/// use std::io;
-/// use std::num;
-///
-/// enum CliError {
-/// IoError(io::Error),
-/// ParseError(num::ParseIntError),
-/// }
-///
-/// impl From<io::Error> for CliError {
-/// fn from(error: io::Error) -> Self {
-/// CliError::IoError(error)
-/// }
-/// }
-///
-/// impl From<num::ParseIntError> for CliError {
-/// fn from(error: num::ParseIntError) -> Self {
-/// CliError::ParseError(error)
-/// }
-/// }
-///
-/// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
-/// let mut contents = fs::read_to_string(&file_name)?;
-/// let num: i32 = contents.trim().parse()?;
-/// Ok(num)
-/// }
-/// ```
-///
-/// [`TryFrom`]: trait.TryFrom.html
-/// [`Option<T>`]: ../../std/option/enum.Option.html
-/// [`Result<T, E>`]: ../../std/result/enum.Result.html
-/// [`String`]: ../../std/string/struct.String.html
-/// [`Into`]: trait.Into.html
-/// [`from`]: trait.From.html#tymethod.from
-/// [book]: ../../book/ch09-00-error-handling.html
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_on_unimplemented(on(
- all(_Self = "&str", T = "std::string::String"),
- note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
-))]
-pub trait From<T>: Sized {
- /// Performs the conversion.
- #[stable(feature = "rust1", since = "1.0.0")]
- fn from(_: T) -> Self;
-}
-
-/// An attempted conversion that consumes `self`, which may or may not be
-/// expensive.
-///
-/// Library authors should usually not directly implement this trait,
-/// but should prefer implementing the [`TryFrom`] trait, which offers
-/// greater flexibility and provides an equivalent `TryInto`
-/// implementation for free, thanks to a blanket implementation in the
-/// standard library. For more information on this, see the
-/// documentation for [`Into`].
-///
-/// # Implementing `TryInto`
-///
-/// This suffers the same restrictions and reasoning as implementing
-/// [`Into`], see there for details.
-///
-/// [`TryFrom`]: trait.TryFrom.html
-/// [`Into`]: trait.Into.html
-#[stable(feature = "try_from", since = "1.34.0")]
-pub trait TryInto<T>: Sized {
- /// The type returned in the event of a conversion error.
- #[stable(feature = "try_from", since = "1.34.0")]
- type Error;
-
- /// Performs the conversion.
- #[stable(feature = "try_from", since = "1.34.0")]
- fn try_into(self) -> Result<T, Self::Error>;
-}
-
-/// Simple and safe type conversions that may fail in a controlled
-/// way under some circumstances. It is the reciprocal of [`TryInto`].
-///
-/// This is useful when you are doing a type conversion that may
-/// trivially succeed but may also need special handling.
-/// For example, there is no way to convert an [`i64`] into an [`i32`]
-/// using the [`From`] trait, because an [`i64`] may contain a value
-/// that an [`i32`] cannot represent and so the conversion would lose data.
-/// This might be handled by truncating the [`i64`] to an [`i32`] (essentially
-/// giving the [`i64`]'s value modulo [`i32::MAX`]) or by simply returning
-/// [`i32::MAX`], or by some other method. The [`From`] trait is intended
-/// for perfect conversions, so the `TryFrom` trait informs the
-/// programmer when a type conversion could go bad and lets them
-/// decide how to handle it.
-///
-/// # Generic Implementations
-///
-/// - `TryFrom<T> for U` implies [`TryInto`]`<U> for T`
-/// - [`try_from`] is reflexive, which means that `TryFrom<T> for T`
-/// is implemented and cannot fail -- the associated `Error` type for
-/// calling `T::try_from()` on a value of type `T` is [`!`].
-///
-/// `TryFrom<T>` can be implemented as follows:
-///
-/// ```
-/// use std::convert::TryFrom;
-///
-/// struct GreaterThanZero(i32);
-///
-/// impl TryFrom<i32> for GreaterThanZero {
-/// type Error = &'static str;
-///
-/// fn try_from(value: i32) -> Result<Self, Self::Error> {
-/// if value <= 0 {
-/// Err("GreaterThanZero only accepts value superior than zero!")
-/// } else {
-/// Ok(GreaterThanZero(value))
-/// }
-/// }
-/// }
-/// ```
-///
-/// # Examples
-///
-/// As described, [`i32`] implements `TryFrom<`[`i64`]`>`:
-///
-/// ```
-/// use std::convert::TryFrom;
-///
-/// let big_number = 1_000_000_000_000i64;
-/// // Silently truncates `big_number`, requires detecting
-/// // and handling the truncation after the fact.
-/// let smaller_number = big_number as i32;
-/// assert_eq!(smaller_number, -727379968);
-///
-/// // Returns an error because `big_number` is too big to
-/// // fit in an `i32`.
-/// let try_smaller_number = i32::try_from(big_number);
-/// assert!(try_smaller_number.is_err());
-///
-/// // Returns `Ok(3)`.
-/// let try_successful_smaller_number = i32::try_from(3);
-/// assert!(try_successful_smaller_number.is_ok());
-/// ```
-///
-/// [`try_from`]: trait.TryFrom.html#tymethod.try_from
-/// [`TryInto`]: trait.TryInto.html
-/// [`i32::MAX`]: ../../std/i32/constant.MAX.html
-/// [`!`]: ../../std/primitive.never.html
-#[stable(feature = "try_from", since = "1.34.0")]
-pub trait TryFrom<T>: Sized {
- /// The type returned in the event of a conversion error.
- #[stable(feature = "try_from", since = "1.34.0")]
- type Error;
-
- /// Performs the conversion.
- #[stable(feature = "try_from", since = "1.34.0")]
- fn try_from(value: T) -> Result<Self, Self::Error>;
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// GENERIC IMPLS
-////////////////////////////////////////////////////////////////////////////////
-
-// As lifts over &
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsRef<U> for &T
-where
- T: AsRef<U>,
-{
- fn as_ref(&self) -> &U {
- <T as AsRef<U>>::as_ref(*self)
- }
-}
-
-// As lifts over &mut
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsRef<U> for &mut T
-where
- T: AsRef<U>,
-{
- fn as_ref(&self) -> &U {
- <T as AsRef<U>>::as_ref(*self)
- }
-}
-
-// FIXME (#45742): replace the above impls for &/&mut with the following more general one:
-// // As lifts over Deref
-// impl<D: ?Sized + Deref<Target: AsRef<U>>, U: ?Sized> AsRef<U> for D {
-// fn as_ref(&self) -> &U {
-// self.deref().as_ref()
-// }
-// }
-
-// AsMut lifts over &mut
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T
-where
- T: AsMut<U>,
-{
- fn as_mut(&mut self) -> &mut U {
- (*self).as_mut()
- }
-}
-
-// FIXME (#45742): replace the above impl for &mut with the following more general one:
-// // AsMut lifts over DerefMut
-// impl<D: ?Sized + Deref<Target: AsMut<U>>, U: ?Sized> AsMut<U> for D {
-// fn as_mut(&mut self) -> &mut U {
-// self.deref_mut().as_mut()
-// }
-// }
-
-// From implies Into
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T, U> Into<U> for T
-where
- U: From<T>,
-{
- fn into(self) -> U {
- U::from(self)
- }
-}
-
-// From (and thus Into) is reflexive
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> From<T> for T {
- fn from(t: T) -> T {
- t
- }
-}
-
-/// **Stability note:** This impl does not yet exist, but we are
-/// "reserving space" to add it in the future. See
-/// [rust-lang/rust#64715][#64715] for details.
-///
-/// [#64715]: https://github.com/rust-lang/rust/issues/64715
-#[stable(feature = "convert_infallible", since = "1.34.0")]
-#[rustc_reservation_impl = "permitting this impl would forbid us from adding \
- `impl<T> From<!> for T` later; see rust-lang/rust#64715 for details"]
-impl<T> From<!> for T {
- fn from(t: !) -> T {
- t
- }
-}
-
-// TryFrom implies TryInto
-#[stable(feature = "try_from", since = "1.34.0")]
-impl<T, U> TryInto<U> for T
-where
- U: TryFrom<T>,
-{
- type Error = U::Error;
-
- fn try_into(self) -> Result<U, U::Error> {
- U::try_from(self)
- }
-}
-
-// Infallible conversions are semantically equivalent to fallible conversions
-// with an uninhabited error type.
-#[stable(feature = "try_from", since = "1.34.0")]
-impl<T, U> TryFrom<U> for T
-where
- U: Into<T>,
-{
- type Error = Infallible;
-
- fn try_from(value: U) -> Result<Self, Self::Error> {
- Ok(U::into(value))
- }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// CONCRETE IMPLS
-////////////////////////////////////////////////////////////////////////////////
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> AsRef<[T]> for [T] {
- fn as_ref(&self) -> &[T] {
- self
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> AsMut<[T]> for [T] {
- fn as_mut(&mut self) -> &mut [T] {
- self
- }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl AsRef<str> for str {
- #[inline]
- fn as_ref(&self) -> &str {
- self
- }
-}
-
-////////////////////////////////////////////////////////////////////////////////
-// THE NO-ERROR ERROR TYPE
-////////////////////////////////////////////////////////////////////////////////
-
-/// A type alias for [the `!` “never” type][never].
-///
-/// `Infallible` represents types of errors that can never happen since `!` has no valid values.
-/// This can be useful for generic APIs that use [`Result`] and parameterize the error type,
-/// to indicate that the result is always [`Ok`].
-///
-/// For example, the [`TryFrom`] trait (conversion that returns a [`Result`])
-/// has a blanket implementation for all types where a reverse [`Into`] implementation exists.
-///
-/// ```ignore (illustrates std code, duplicating the impl in a doctest would be an error)
-/// impl<T, U> TryFrom<U> for T where U: Into<T> {
-/// type Error = Infallible;
-///
-/// fn try_from(value: U) -> Result<Self, Infallible> {
-/// Ok(U::into(value)) // Never returns `Err`
-/// }
-/// }
-/// ```
-///
-/// # Eventual deprecation
-///
-/// Previously, `Infallible` was defined as `enum Infallible {}`.
-/// Now that it is merely a type alias to `!`, we will eventually deprecate `Infallible`.
-///
-/// [`Ok`]: ../result/enum.Result.html#variant.Ok
-/// [`Result`]: ../result/enum.Result.html
-/// [`TryFrom`]: trait.TryFrom.html
-/// [`Into`]: trait.Into.html
-/// [never]: ../../std/primitive.never.html
-#[stable(feature = "convert_infallible", since = "1.34.0")]
-pub type Infallible = !;
--- /dev/null
+//! Traits for conversions between types.
+//!
+//! The traits in this module provide a way to convert from one type to another type.
+//! Each trait serves a different purpose:
+//!
+//! - Implement the [`AsRef`] trait for cheap reference-to-reference conversions
+//! - Implement the [`AsMut`] trait for cheap mutable-to-mutable conversions
+//! - Implement the [`From`] trait for consuming value-to-value conversions
+//! - Implement the [`Into`] trait for consuming value-to-value conversions to types
+//! outside the current crate
+//! - The [`TryFrom`] and [`TryInto`] traits behave like [`From`] and [`Into`],
+//! but should be implemented when the conversion can fail.
+//!
+//! The traits in this module are often used as trait bounds for generic functions such that to
+//! arguments of multiple types are supported. See the documentation of each trait for examples.
+//!
+//! As a library author, you should always prefer implementing [`From<T>`][`From`] or
+//! [`TryFrom<T>`][`TryFrom`] rather than [`Into<U>`][`Into`] or [`TryInto<U>`][`TryInto`],
+//! as [`From`] and [`TryFrom`] provide greater flexibility and offer
+//! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a
+//! blanket implementation in the standard library. Only implement [`Into`] or [`TryInto`]
+//! when a conversion to a type outside the current crate is required.
+//!
+//! # Generic Implementations
+//!
+//! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference
+//! - [`From`]`<U> for T` implies [`Into`]`<T> for U`
+//! - [`TryFrom`]`<U> for T` implies [`TryInto`]`<T> for U`
+//! - [`From`] and [`Into`] are reflexive, which means that all types can
+//! `into` themselves and `from` themselves
+//!
+//! See each trait for usage examples.
+//!
+//! [`Into`]: trait.Into.html
+//! [`From`]: trait.From.html
+//! [`TryFrom`]: trait.TryFrom.html
+//! [`TryInto`]: trait.TryInto.html
+//! [`AsRef`]: trait.AsRef.html
+//! [`AsMut`]: trait.AsMut.html
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+/// The identity function.
+///
+/// Two things are important to note about this function:
+///
+/// - It is not always equivalent to a closure like `|x| x`, since the
+/// closure may coerce `x` into a different type.
+///
+/// - It moves the input `x` passed to the function.
+///
+/// While it might seem strange to have a function that just returns back the
+/// input, there are some interesting uses.
+///
+/// # Examples
+///
+/// Using `identity` to do nothing in a sequence of other, interesting,
+/// functions:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// fn manipulation(x: u32) -> u32 {
+/// // Let's pretend that adding one is an interesting function.
+/// x + 1
+/// }
+///
+/// let _arr = &[identity, manipulation];
+/// ```
+///
+/// Using `identity` as a "do nothing" base case in a conditional:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// # let condition = true;
+/// #
+/// # fn manipulation(x: u32) -> u32 { x + 1 }
+/// #
+/// let do_stuff = if condition { manipulation } else { identity };
+///
+/// // Do more interesting stuff...
+///
+/// let _results = do_stuff(42);
+/// ```
+///
+/// Using `identity` to keep the `Some` variants of an iterator of `Option<T>`:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// let iter = vec![Some(1), None, Some(3)].into_iter();
+/// let filtered = iter.filter_map(identity).collect::<Vec<_>>();
+/// assert_eq!(vec![1, 3], filtered);
+/// ```
+#[stable(feature = "convert_id", since = "1.33.0")]
+#[inline]
+pub const fn identity<T>(x: T) -> T {
+ x
+}
+
+/// Used to do a cheap reference-to-reference conversion.
+///
+/// This trait is similar to [`AsMut`] which is used for converting between mutable references.
+/// If you need to do a costly conversion it is better to implement [`From`] with type
+/// `&T` or write a custom function.
+///
+/// `AsRef` has the same signature as [`Borrow`], but [`Borrow`] is different in few aspects:
+///
+/// - Unlike `AsRef`, [`Borrow`] has a blanket impl for any `T`, and can be used to accept either
+/// a reference or a value.
+/// - [`Borrow`] also requires that [`Hash`], [`Eq`] and [`Ord`] for borrowed value are
+/// equivalent to those of the owned value. For this reason, if you want to
+/// borrow only a single field of a struct you can implement `AsRef`, but not [`Borrow`].
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use a
+/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
+///
+/// # Generic Implementations
+///
+/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
+/// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type
+/// `&mut Foo` or `&&mut Foo`)
+///
+/// # Examples
+///
+/// By using trait bounds we can accept arguments of different types as long as they can be
+/// converted to the specified type `T`.
+///
+/// For example: By creating a generic function that takes an `AsRef<str>` we express that we
+/// want to accept all references that can be converted to [`&str`] as an argument.
+/// Since both [`String`] and [`&str`] implement `AsRef<str>` we can accept both as input argument.
+///
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
+/// [`Hash`]: ../../std/hash/trait.Hash.html
+/// [`Eq`]: ../../std/cmp/trait.Eq.html
+/// [`Ord`]: ../../std/cmp/trait.Ord.html
+/// [`&str`]: ../../std/primitive.str.html
+/// [`String`]: ../../std/string/struct.String.html
+///
+/// ```
+/// fn is_hello<T: AsRef<str>>(s: T) {
+/// assert_eq!("hello", s.as_ref());
+/// }
+///
+/// let s = "hello";
+/// is_hello(s);
+///
+/// let s = "hello".to_string();
+/// is_hello(s);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait AsRef<T: ?Sized> {
+ /// Performs the conversion.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ fn as_ref(&self) -> &T;
+}
+
+/// Used to do a cheap mutable-to-mutable reference conversion.
+///
+/// This trait is similar to [`AsRef`] but used for converting between mutable
+/// references. If you need to do a costly conversion it is better to
+/// implement [`From`] with type `&mut T` or write a custom function.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use a
+/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
+///
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+///
+/// # Generic Implementations
+///
+/// - `AsMut` auto-dereferences if the inner type is a mutable reference
+/// (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo`
+/// or `&mut &mut Foo`)
+///
+/// # Examples
+///
+/// Using `AsMut` as trait bound for a generic function we can accept all mutable references
+/// that can be converted to type `&mut T`. Because [`Box<T>`] implements `AsMut<T>` we can
+/// write a function `add_one` that takes all arguments that can be converted to `&mut u64`.
+/// Because [`Box<T>`] implements `AsMut<T>`, `add_one` accepts arguments of type
+/// `&mut Box<u64>` as well:
+///
+/// ```
+/// fn add_one<T: AsMut<u64>>(num: &mut T) {
+/// *num.as_mut() += 1;
+/// }
+///
+/// let mut boxed_num = Box::new(0);
+/// add_one(&mut boxed_num);
+/// assert_eq!(*boxed_num, 1);
+/// ```
+///
+/// [`Box<T>`]: ../../std/boxed/struct.Box.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait AsMut<T: ?Sized> {
+ /// Performs the conversion.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ fn as_mut(&mut self) -> &mut T;
+}
+
+/// A value-to-value conversion that consumes the input value. The
+/// opposite of [`From`].
+///
+/// One should avoid implementing [`Into`] and implement [`From`] instead.
+/// Implementing [`From`] automatically provides one with an implementation of [`Into`]
+/// thanks to the blanket implementation in the standard library.
+///
+/// Prefer using [`Into`] over [`From`] when specifying trait bounds on a generic function
+/// to ensure that types that only implement [`Into`] can be used as well.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use [`TryInto`].
+///
+/// # Generic Implementations
+///
+/// - [`From`]`<T> for U` implies `Into<U> for T`
+/// - [`Into`] is reflexive, which means that `Into<T> for T` is implemented
+///
+/// # Implementing [`Into`] for conversions to external types in old versions of Rust
+///
+/// Prior to Rust 1.40, if the destination type was not part of the current crate
+/// then you couldn't implement [`From`] directly.
+/// For example, take this code:
+///
+/// ```
+/// struct Wrapper<T>(Vec<T>);
+/// impl<T> From<Wrapper<T>> for Vec<T> {
+/// fn from(w: Wrapper<T>) -> Vec<T> {
+/// w.0
+/// }
+/// }
+/// ```
+/// This will fail to compile in older versions of the language because Rust's orphaning rules
+/// used to be a little bit more strict. To bypass this, you could implement [`Into`] directly:
+///
+/// ```
+/// struct Wrapper<T>(Vec<T>);
+/// impl<T> Into<Vec<T>> for Wrapper<T> {
+/// fn into(self) -> Vec<T> {
+/// self.0
+/// }
+/// }
+/// ```
+///
+/// It is important to understand that [`Into`] does not provide a [`From`] implementation
+/// (as [`From`] does with [`Into`]). Therefore, you should always try to implement [`From`]
+/// and then fall back to [`Into`] if [`From`] can't be implemented.
+///
+/// # Examples
+///
+/// [`String`] implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>`:
+///
+/// In order to express that we want a generic function to take all arguments that can be
+/// converted to a specified type `T`, we can use a trait bound of [`Into`]`<T>`.
+/// For example: The function `is_hello` takes all arguments that can be converted into a
+/// [`Vec`]`<`[`u8`]`>`.
+///
+/// ```
+/// fn is_hello<T: Into<Vec<u8>>>(s: T) {
+/// let bytes = b"hello".to_vec();
+/// assert_eq!(bytes, s.into());
+/// }
+///
+/// let s = "hello".to_string();
+/// is_hello(s);
+/// ```
+///
+/// [`TryInto`]: trait.TryInto.html
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`String`]: ../../std/string/struct.String.html
+/// [`From`]: trait.From.html
+/// [`Into`]: trait.Into.html
+/// [`Vec`]: ../../std/vec/struct.Vec.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Into<T>: Sized {
+ /// Performs the conversion.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ fn into(self) -> T;
+}
+
+/// Used to do value-to-value conversions while consuming the input value. It is the reciprocal of
+/// [`Into`].
+///
+/// One should always prefer implementing `From` over [`Into`]
+/// because implementing `From` automatically provides one with a implementation of [`Into`]
+/// thanks to the blanket implementation in the standard library.
+///
+/// Only implement [`Into`] if a conversion to a type outside the current crate is required.
+/// `From` cannot do these type of conversions because of Rust's orphaning rules.
+/// See [`Into`] for more details.
+///
+/// Prefer using [`Into`] over using `From` when specifying trait bounds on a generic function.
+/// This way, types that directly implement [`Into`] can be used as arguments as well.
+///
+/// The `From` is also very useful when performing error handling. When constructing a function
+/// that is capable of failing, the return type will generally be of the form `Result<T, E>`.
+/// The `From` trait simplifies error handling by allowing a function to return a single error type
+/// that encapsulate multiple error types. See the "Examples" section and [the book][book] for more
+/// details.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use [`TryFrom`].
+///
+/// # Generic Implementations
+///
+/// - `From<T> for U` implies [`Into`]`<U> for T`
+/// - `From` is reflexive, which means that `From<T> for T` is implemented
+///
+/// # Examples
+///
+/// [`String`] implements `From<&str>`:
+///
+/// An explicit conversion from a `&str` to a String is done as follows:
+///
+/// ```
+/// let string = "hello".to_string();
+/// let other_string = String::from("hello");
+///
+/// assert_eq!(string, other_string);
+/// ```
+///
+/// While performing error handling it is often useful to implement `From` for your own error type.
+/// By converting underlying error types to our own custom error type that encapsulates the
+/// underlying error type, we can return a single error type without losing information on the
+/// underlying cause. The '?' operator automatically converts the underlying error type to our
+/// custom error type by calling `Into<CliError>::into` which is automatically provided when
+/// implementing `From`. The compiler then infers which implementation of `Into` should be used.
+///
+/// ```
+/// use std::fs;
+/// use std::io;
+/// use std::num;
+///
+/// enum CliError {
+/// IoError(io::Error),
+/// ParseError(num::ParseIntError),
+/// }
+///
+/// impl From<io::Error> for CliError {
+/// fn from(error: io::Error) -> Self {
+/// CliError::IoError(error)
+/// }
+/// }
+///
+/// impl From<num::ParseIntError> for CliError {
+/// fn from(error: num::ParseIntError) -> Self {
+/// CliError::ParseError(error)
+/// }
+/// }
+///
+/// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
+/// let mut contents = fs::read_to_string(&file_name)?;
+/// let num: i32 = contents.trim().parse()?;
+/// Ok(num)
+/// }
+/// ```
+///
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`String`]: ../../std/string/struct.String.html
+/// [`Into`]: trait.Into.html
+/// [`from`]: trait.From.html#tymethod.from
+/// [book]: ../../book/ch09-00-error-handling.html
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented(on(
+ all(_Self = "&str", T = "std::string::String"),
+ note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
+))]
+pub trait From<T>: Sized {
+ /// Performs the conversion.
+ #[stable(feature = "rust1", since = "1.0.0")]
+ fn from(_: T) -> Self;
+}
+
+/// An attempted conversion that consumes `self`, which may or may not be
+/// expensive.
+///
+/// Library authors should usually not directly implement this trait,
+/// but should prefer implementing the [`TryFrom`] trait, which offers
+/// greater flexibility and provides an equivalent `TryInto`
+/// implementation for free, thanks to a blanket implementation in the
+/// standard library. For more information on this, see the
+/// documentation for [`Into`].
+///
+/// # Implementing `TryInto`
+///
+/// This suffers the same restrictions and reasoning as implementing
+/// [`Into`], see there for details.
+///
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Into`]: trait.Into.html
+#[stable(feature = "try_from", since = "1.34.0")]
+pub trait TryInto<T>: Sized {
+ /// The type returned in the event of a conversion error.
+ #[stable(feature = "try_from", since = "1.34.0")]
+ type Error;
+
+ /// Performs the conversion.
+ #[stable(feature = "try_from", since = "1.34.0")]
+ fn try_into(self) -> Result<T, Self::Error>;
+}
+
+/// Simple and safe type conversions that may fail in a controlled
+/// way under some circumstances. It is the reciprocal of [`TryInto`].
+///
+/// This is useful when you are doing a type conversion that may
+/// trivially succeed but may also need special handling.
+/// For example, there is no way to convert an [`i64`] into an [`i32`]
+/// using the [`From`] trait, because an [`i64`] may contain a value
+/// that an [`i32`] cannot represent and so the conversion would lose data.
+/// This might be handled by truncating the [`i64`] to an [`i32`] (essentially
+/// giving the [`i64`]'s value modulo [`i32::MAX`]) or by simply returning
+/// [`i32::MAX`], or by some other method. The [`From`] trait is intended
+/// for perfect conversions, so the `TryFrom` trait informs the
+/// programmer when a type conversion could go bad and lets them
+/// decide how to handle it.
+///
+/// # Generic Implementations
+///
+/// - `TryFrom<T> for U` implies [`TryInto`]`<U> for T`
+/// - [`try_from`] is reflexive, which means that `TryFrom<T> for T`
+/// is implemented and cannot fail -- the associated `Error` type for
+/// calling `T::try_from()` on a value of type `T` is [`!`].
+///
+/// `TryFrom<T>` can be implemented as follows:
+///
+/// ```
+/// use std::convert::TryFrom;
+///
+/// struct GreaterThanZero(i32);
+///
+/// impl TryFrom<i32> for GreaterThanZero {
+/// type Error = &'static str;
+///
+/// fn try_from(value: i32) -> Result<Self, Self::Error> {
+/// if value <= 0 {
+/// Err("GreaterThanZero only accepts value superior than zero!")
+/// } else {
+/// Ok(GreaterThanZero(value))
+/// }
+/// }
+/// }
+/// ```
+///
+/// # Examples
+///
+/// As described, [`i32`] implements `TryFrom<`[`i64`]`>`:
+///
+/// ```
+/// use std::convert::TryFrom;
+///
+/// let big_number = 1_000_000_000_000i64;
+/// // Silently truncates `big_number`, requires detecting
+/// // and handling the truncation after the fact.
+/// let smaller_number = big_number as i32;
+/// assert_eq!(smaller_number, -727379968);
+///
+/// // Returns an error because `big_number` is too big to
+/// // fit in an `i32`.
+/// let try_smaller_number = i32::try_from(big_number);
+/// assert!(try_smaller_number.is_err());
+///
+/// // Returns `Ok(3)`.
+/// let try_successful_smaller_number = i32::try_from(3);
+/// assert!(try_successful_smaller_number.is_ok());
+/// ```
+///
+/// [`try_from`]: trait.TryFrom.html#tymethod.try_from
+/// [`TryInto`]: trait.TryInto.html
+/// [`i32::MAX`]: ../../std/i32/constant.MAX.html
+/// [`!`]: ../../std/primitive.never.html
+#[stable(feature = "try_from", since = "1.34.0")]
+pub trait TryFrom<T>: Sized {
+ /// The type returned in the event of a conversion error.
+ #[stable(feature = "try_from", since = "1.34.0")]
+ type Error;
+
+ /// Performs the conversion.
+ #[stable(feature = "try_from", since = "1.34.0")]
+ fn try_from(value: T) -> Result<Self, Self::Error>;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// GENERIC IMPLS
+////////////////////////////////////////////////////////////////////////////////
+
+// As lifts over &
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsRef<U> for &T
+where
+ T: AsRef<U>,
+{
+ fn as_ref(&self) -> &U {
+ <T as AsRef<U>>::as_ref(*self)
+ }
+}
+
+// As lifts over &mut
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsRef<U> for &mut T
+where
+ T: AsRef<U>,
+{
+ fn as_ref(&self) -> &U {
+ <T as AsRef<U>>::as_ref(*self)
+ }
+}
+
+// FIXME (#45742): replace the above impls for &/&mut with the following more general one:
+// // As lifts over Deref
+// impl<D: ?Sized + Deref<Target: AsRef<U>>, U: ?Sized> AsRef<U> for D {
+// fn as_ref(&self) -> &U {
+// self.deref().as_ref()
+// }
+// }
+
+// AsMut lifts over &mut
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T
+where
+ T: AsMut<U>,
+{
+ fn as_mut(&mut self) -> &mut U {
+ (*self).as_mut()
+ }
+}
+
+// FIXME (#45742): replace the above impl for &mut with the following more general one:
+// // AsMut lifts over DerefMut
+// impl<D: ?Sized + Deref<Target: AsMut<U>>, U: ?Sized> AsMut<U> for D {
+// fn as_mut(&mut self) -> &mut U {
+// self.deref_mut().as_mut()
+// }
+// }
+
+// From implies Into
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, U> Into<U> for T
+where
+ U: From<T>,
+{
+ fn into(self) -> U {
+ U::from(self)
+ }
+}
+
+// From (and thus Into) is reflexive
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> From<T> for T {
+ fn from(t: T) -> T {
+ t
+ }
+}
+
+/// **Stability note:** This impl does not yet exist, but we are
+/// "reserving space" to add it in the future. See
+/// [rust-lang/rust#64715][#64715] for details.
+///
+/// [#64715]: https://github.com/rust-lang/rust/issues/64715
+#[stable(feature = "convert_infallible", since = "1.34.0")]
+#[rustc_reservation_impl = "permitting this impl would forbid us from adding \
+ `impl<T> From<!> for T` later; see rust-lang/rust#64715 for details"]
+impl<T> From<!> for T {
+ fn from(t: !) -> T {
+ t
+ }
+}
+
+// TryFrom implies TryInto
+#[stable(feature = "try_from", since = "1.34.0")]
+impl<T, U> TryInto<U> for T
+where
+ U: TryFrom<T>,
+{
+ type Error = U::Error;
+
+ fn try_into(self) -> Result<U, U::Error> {
+ U::try_from(self)
+ }
+}
+
+// Infallible conversions are semantically equivalent to fallible conversions
+// with an uninhabited error type.
+#[stable(feature = "try_from", since = "1.34.0")]
+impl<T, U> TryFrom<U> for T
+where
+ U: Into<T>,
+{
+ type Error = Infallible;
+
+ fn try_from(value: U) -> Result<Self, Self::Error> {
+ Ok(U::into(value))
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// CONCRETE IMPLS
+////////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<[T]> for [T] {
+ fn as_ref(&self) -> &[T] {
+ self
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsMut<[T]> for [T] {
+ fn as_mut(&mut self) -> &mut [T] {
+ self
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl AsRef<str> for str {
+ #[inline]
+ fn as_ref(&self) -> &str {
+ self
+ }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// THE NO-ERROR ERROR TYPE
+////////////////////////////////////////////////////////////////////////////////
+
+/// A type alias for [the `!` “never” type][never].
+///
+/// `Infallible` represents types of errors that can never happen since `!` has no valid values.
+/// This can be useful for generic APIs that use [`Result`] and parameterize the error type,
+/// to indicate that the result is always [`Ok`].
+///
+/// For example, the [`TryFrom`] trait (conversion that returns a [`Result`])
+/// has a blanket implementation for all types where a reverse [`Into`] implementation exists.
+///
+/// ```ignore (illustrates std code, duplicating the impl in a doctest would be an error)
+/// impl<T, U> TryFrom<U> for T where U: Into<T> {
+/// type Error = Infallible;
+///
+/// fn try_from(value: U) -> Result<Self, Infallible> {
+/// Ok(U::into(value)) // Never returns `Err`
+/// }
+/// }
+/// ```
+///
+/// # Eventual deprecation
+///
+/// Previously, `Infallible` was defined as `enum Infallible {}`.
+/// Now that it is merely a type alias to `!`, we will eventually deprecate `Infallible`.
+///
+/// [`Ok`]: ../result/enum.Result.html#variant.Ok
+/// [`Result`]: ../result/enum.Result.html
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Into`]: trait.Into.html
+/// [never]: ../../std/primitive.never.html
+#[stable(feature = "convert_infallible", since = "1.34.0")]
+pub type Infallible = !;
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