Rollup merge of #39165 - frewsxcv:slice, r=GuillaumeGomez

A few improvements to the slice docs. * Simplify `Option::iter_mut` doc example. * Document 'empty' corner-cases for `slice::{starts_with, ends_with}`. * Indicate 'true' as code-like.

Author: GuillaumeGomez

src/libcollections/slice.rs

@@ -181,7 +181,7 @@ impl<T> [T] {
  core_slice::SliceExt::len(self)
  }
 
- /// Returns true if the slice has a length of 0.
+ /// Returns `true` if the slice has a length of 0.
  ///
  /// # Example
  ///
@@ -549,12 +549,8 @@ impl<T> [T] {
  ///
  /// ```
  /// let x = &mut [1, 2, 4];
- /// {
- /// let iterator = x.iter_mut();
- ///
- /// for elem in iterator {
- /// *elem += 2;
- /// }
+ /// for elem in x.iter_mut() {
+ /// *elem += 2;
  /// }
  /// assert_eq!(x, &[3, 4, 6]);
  /// ```
@@ -889,7 +885,7 @@ impl<T> [T] {
  core_slice::SliceExt::rsplitn_mut(self, n, pred)
  }
 
- /// Returns true if the slice contains an element with the given value.
+ /// Returns `true` if the slice contains an element with the given value.
  ///
  /// # Examples
  ///
@@ -905,7 +901,7 @@ impl<T> [T] {
  core_slice::SliceExt::contains(self, x)
  }
 
- /// Returns true if `needle` is a prefix of the slice.
+ /// Returns `true` if `needle` is a prefix of the slice.
  ///
  /// # Examples
  ///
@@ -916,14 +912,23 @@ impl<T> [T] {
  /// assert!(!v.starts_with(&[50]));
  /// assert!(!v.starts_with(&[10, 50]));
  /// ```
+ ///
+ /// Always returns `true` if `needle` is an empty slice:
+ ///
+ /// ```
+ /// let v = &[10, 40, 30];
+ /// assert!(v.starts_with(&[]));
+ /// let v: &[u8] = &[];
+ /// assert!(v.starts_with(&[]));
+ /// ```
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn starts_with(&self, needle: &[T]) -> bool
  where T: PartialEq
  {
  core_slice::SliceExt::starts_with(self, needle)
  }
 
- /// Returns true if `needle` is a suffix of the slice.
+ /// Returns `true` if `needle` is a suffix of the slice.
  ///
  /// # Examples
  ///
@@ -934,6 +939,15 @@ impl<T> [T] {
  /// assert!(!v.ends_with(&[50]));
  /// assert!(!v.ends_with(&[50, 30]));
  /// ```
+ ///
+ /// Always returns `true` if `needle` is an empty slice:
+ ///
+ /// ```
+ /// let v = &[10, 40, 30];
+ /// assert!(v.ends_with(&[]));
+ /// let v: &[u8] = &[];
+ /// assert!(v.ends_with(&[]));
+ /// ```
  #[stable(feature = "rust1", since = "1.0.0")]
  pub fn ends_with(&self, needle: &[T]) -> bool
  where T: PartialEq