diff options
Diffstat (limited to 'src/libcore/convert.rs')
| -rw-r--r-- | src/libcore/convert.rs | 95 |
1 files changed, 7 insertions, 88 deletions
diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs index e16c3840260..89a269bdb8e 100644 --- a/src/libcore/convert.rs +++ b/src/libcore/convert.rs @@ -40,8 +40,6 @@ #![stable(feature = "rust1", since = "1.0.0")] -use crate::fmt; - /// The identity function. /// /// Two things are important to note about this function: @@ -426,9 +424,7 @@ pub trait TryInto<T>: Sized { /// - `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 [`Infallible`]. -/// When the [`!`] type is stabilized [`Infallible`] and [`!`] will be -/// equivalent. +/// calling `T::try_from()` on a value of type `T` is [`!`]. /// /// `TryFrom<T>` can be implemented as follows: /// @@ -477,7 +473,6 @@ pub trait TryInto<T>: Sized { /// [`TryInto`]: trait.TryInto.html /// [`i32::MAX`]: ../../std/i32/constant.MAX.html /// [`!`]: ../../std/primitive.never.html -/// [`Infallible`]: enum.Infallible.html #[stable(feature = "try_from", since = "1.34.0")] pub trait TryFrom<T>: Sized { /// The type returned in the event of a conversion error. @@ -615,9 +610,9 @@ impl AsRef<str> for str { // THE NO-ERROR ERROR TYPE //////////////////////////////////////////////////////////////////////////////// -/// The error type for errors that can never happen. +/// A type alias for [the `!` “never” type][never]. /// -/// Since this enum has no variant, a value of this type can never actually exist. +/// `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`]. /// @@ -634,33 +629,10 @@ impl AsRef<str> for str { /// } /// ``` /// -/// # Future compatibility -/// -/// This enum has the same role as [the `!` “never” type][never], -/// which is unstable in this version of Rust. -/// When `!` is stabilized, we plan to make `Infallible` a type alias to it: -/// -/// ```ignore (illustrates future std change) -/// pub type Infallible = !; -/// ``` -/// -/// … and eventually deprecate `Infallible`. -/// -/// -/// However there is one case where `!` syntax can be used -/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type. -/// Specifically, it is possible implementations for two different function pointer types: -/// -/// ``` -/// trait MyTrait {} -/// impl MyTrait for fn() -> ! {} -/// impl MyTrait for fn() -> std::convert::Infallible {} -/// ``` +/// # Eventual deprecation /// -/// With `Infallible` being an enum, this code is valid. -/// However when `Infallible` becomes an alias for the never type, -/// the two `impl`s will start to overlap -/// and therefore will be disallowed by the language’s trait coherence rules. +/// 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 @@ -668,57 +640,4 @@ impl AsRef<str> for str { /// [`Into`]: trait.Into.html /// [never]: ../../std/primitive.never.html #[stable(feature = "convert_infallible", since = "1.34.0")] -#[derive(Copy)] -pub enum Infallible {} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl Clone for Infallible { - fn clone(&self) -> Infallible { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl fmt::Debug for Infallible { - fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl fmt::Display for Infallible { - fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl PartialEq for Infallible { - fn eq(&self, _: &Infallible) -> bool { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl Eq for Infallible {} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl PartialOrd for Infallible { - fn partial_cmp(&self, _other: &Self) -> Option<crate::cmp::Ordering> { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl Ord for Infallible { - fn cmp(&self, _other: &Self) -> crate::cmp::Ordering { - match *self {} - } -} - -#[stable(feature = "convert_infallible", since = "1.34.0")] -impl From<!> for Infallible { - fn from(x: !) -> Self { - x - } -} +pub type Infallible = !; |