Rollup merge of rust-lang#39886 - mbrubeck:doc-edit, r=steveklabnik

Additional docs for Vec, String, and slice trait impls

r? @steveklabnik

src/libcollections/string.rs

@@ -1629,6 +1629,43 @@ impl hash::Hash for String {
     }
 }
 
+/// Implements the `+` operator for concatenating two strings.
+///
+/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
+/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
+/// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
+/// repeated concatenation.
+///
+/// The string on the right-hand side is only borrowed; its contents are copied into the returned
+/// `String`.
+///
+/// # Examples
+///
+/// Concatenating two `String`s takes the first by value and borrows the second:
+///
+/// ```
+/// let a = String::from("hello");
+/// let b = String::from(" world");
+/// let c = a + &b;
+/// // `a` is moved and can no longer be used here.
+/// ```
+///
+/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
+///
+/// ```
+/// let a = String::from("hello");
+/// let b = String::from(" world");
+/// let c = a.clone() + &b;
+/// // `a` is still valid here.
+/// ```
+///
+/// Concatenating `&str` slices can be done by converting the first to a `String`:
+///
+/// ```
+/// let a = "hello";
+/// let b = " world";
+/// let c = a.to_string() + b;
+/// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Add<&'a str> for String {
     type Output = String;
@@ -1640,6 +1677,11 @@ impl<'a> Add<&'a str> for String {
     }
 }
 
+/// Implements the `+=` operator for appending to a `String`.
+///
+/// This has the same behavior as the [`push_str()`] method.
+///
+/// [`push_str()`]: struct.String.html#method.push_str
 #[stable(feature = "stringaddassign", since = "1.12.0")]
 impl<'a> AddAssign<&'a str> for String {
     #[inline]

src/libcollections/vec.rs

@@ -1776,6 +1776,7 @@ array_impls! {
     30 31 32
 }
 
+/// Implements comparison of vectors, lexicographically.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: PartialOrd> PartialOrd for Vec<T> {
     #[inline]
@@ -1787,6 +1788,7 @@ impl<T: PartialOrd> PartialOrd for Vec<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Eq> Eq for Vec<T> {}
 
+/// Implements ordering of vectors, lexicographically.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> Ord for Vec<T> {
     #[inline]

src/libcore/slice.rs

@@ -2202,13 +2202,15 @@ impl<A, B> PartialEq<[B]> for [A] where A: PartialEq<B> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Eq> Eq for [T] {}
 
+/// Implements comparison of vectors lexicographically.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> Ord for [T] {
     fn cmp(&self, other: &[T]) -> Ordering {
         SliceOrd::compare(self, other)
     }
 }
 
+/// Implements comparison of vectors lexicographically.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: PartialOrd> PartialOrd for [T] {
     fn partial_cmp(&self, other: &[T]) -> Option<Ordering> {

src/libcore/str/mod.rs

@@ -1366,6 +1366,13 @@ mod traits {
     use ops;
     use str::eq_slice;
 
+    /// Implements ordering of strings.
+    ///
+    /// Strings are ordered  lexicographically by their byte values.  This orders Unicode code
+    /// points based on their positions in the code charts.  This is not necessarily the same as
+    /// "alphabetical" order, which varies by language and locale.  Sorting strings according to
+    /// culturally-accepted standards requires locale-specific data that is outside the scope of
+    /// the `str` type.
     #[stable(feature = "rust1", since = "1.0.0")]
     impl Ord for str {
         #[inline]
@@ -1387,6 +1394,13 @@ mod traits {
     #[stable(feature = "rust1", since = "1.0.0")]
     impl Eq for str {}
 
+    /// Implements comparison operations on strings.
+    ///
+    /// Strings are compared lexicographically by their byte values.  This compares Unicode code
+    /// points based on their positions in the code charts.  This is not necessarily the same as
+    /// "alphabetical" order, which varies by language and locale.  Comparing strings according to
+    /// culturally-accepted standards requires locale-specific data that is outside the scope of
+    /// the `str` type.
     #[stable(feature = "rust1", since = "1.0.0")]
     impl PartialOrd for str {
         #[inline]