Rollup merge of #73447 - lzutao:stabilize-result_as_deref, r=dtolnay

Improve document for `Result::as_deref(_mut)` methods

cc #50264

Author: RalfJung

src/libcore/result.rs

@@ -1145,45 +1145,69 @@ impl<T, E: Into<!>> Result<T, E> {
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T: Deref, E> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T::Target, &E>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&<T as Deref>::Target, &E>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
-    /// `Ok` type's `Deref::Target` type.
+    /// Coerces the [`Ok`] variant of the original [`Result`] via [`Deref`](crate::ops::Deref)
+    /// and returns the new [`Result`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<String, u32> = Ok("hello".to_string());
+    /// let y: Result<&str, &u32> = Ok("hello");
+    /// assert_eq!(x.as_deref(), y);
+    ///
+    /// let x: Result<String, u32> = Err(42);
+    /// let y: Result<&str, &u32> = Err(&42);
+    /// assert_eq!(x.as_deref(), y);
+    /// ```
     pub fn as_deref(&self) -> Result<&T::Target, &E> {
         self.as_ref().map(|t| t.deref())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T, E: Deref> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T, &E::Target>`.
+    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&T, &<E as Deref>::Target>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a reference to the
-    /// `Err` type's `Deref::Target` type.
+    /// Coerces the [`Err`] variant of the original [`Result`] via [`Deref`](crate::ops::Deref)
+    /// and returns the new [`Result`].
     pub fn as_deref_err(&self) -> Result<&T, &E::Target> {
         self.as_ref().map_err(|e| e.deref())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T: DerefMut, E> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T::Target, &mut E>`.
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut <T as DerefMut>::Target, &mut E>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
-    /// the `Ok` type's `Deref::Target` type.
+    /// Coerces the [`Ok`] variant of the original [`Result`] via [`DerefMut`](crate::ops::DerefMut)
+    /// and returns the new [`Result`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut x: Result<String, u32> = Ok("hello".to_string());
+    /// let y: Result<&mut str, &mut u32> = Ok("HELLO");
+    /// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
+    ///
+    /// let mut x: Result<String, u32> = Err(42);
+    /// let y: Result<&mut str, &mut u32> = Err(&42);
+    /// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
+    /// ```
     pub fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E> {
         self.as_mut().map(|t| t.deref_mut())
     }
 }
 
-#[unstable(feature = "inner_deref", reason = "newly added", issue = "50264")]
+#[unstable(feature = "inner_deref", issue = "50264")]
 impl<T, E: DerefMut> Result<T, E> {
-    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T, &mut E::Target>`.
+    /// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut T, &mut <E as DerefMut>::Target>`.
     ///
-    /// Leaves the original `Result` in-place, creating a new one containing a mutable reference to
-    /// the `Err` type's `Deref::Target` type.
+    /// Coerces the [`Err`] variant of the original [`Result`] via [`DerefMut`](crate::ops::DerefMut)
+    /// and returns the new [`Result`].
     pub fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target> {
         self.as_mut().map_err(|e| e.deref_mut())
     }