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Rollup merge of #51312 - frewsxcv:clarify-hash-map-entry-get-mut, r=dtolnay

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Clarify the difference between get_mut and into_mut for OccupiedEntry

The examples for both hash_map::OccupiedEntry::get_mut and
hash_map::OccupiedEntry::into_mut were almost identical. This led to some
confusion over the difference, namely why you would ever use get_mut when
into_mut gives alonger lifetime. Reddit thread:
https://www.reddit.com/r/rust/comments/8a5swr/why_does_hashmaps

This commit adds two lines and a comment to the example, to show that the
entry object can be re-used after calling get_mut.

Closes https://github.com/rust-lang/rust/issues/49745
This commit is contained in:
Mark Simulacrum 2018-06-02 19:55:09 -06:00 committed by GitHub
commit a689b2d8ac
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2 changed files with 30 additions and 4 deletions
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17
src/liballoc/btree/map.rs
View File

@ -2369,6 +2369,11 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
/// Gets a mutable reference to the value in the entry.
///
/// If you need a reference to the `OccupiedEntry` which may outlive the
/// destruction of the `Entry` value, see [`into_mut`].
///
/// [`into_mut`]: #method.into_mut
///
/// # Examples
///
/// ```
@ -2380,9 +2385,13 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
///
/// assert_eq!(map["poneyland"], 12);
/// if let Entry::Occupied(mut o) = map.entry("poneyland") {
/// *o.get_mut() += 10;
/// *o.get_mut() += 10;
/// assert_eq!(*o.get(), 22);
///
/// // We can use the same Entry multiple times.
/// *o.get_mut() += 2;
/// }
/// assert_eq!(map["poneyland"], 22);
/// assert_eq!(map["poneyland"], 24);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn get_mut(&mut self) -> &mut V {
@ -2391,6 +2400,10 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
/// Converts the entry into a mutable reference to its value.
///
/// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
///
/// [`get_mut`]: #method.get_mut
///
/// # Examples
///
/// ```

17
src/libstd/collections/hash/map.rs
View File

@ -2250,6 +2250,11 @@ impl<'a, K, V> OccupiedEntry<'a, K, V> {
/// Gets a mutable reference to the value in the entry.
///
/// If you need a reference to the `OccupiedEntry` which may outlive the
/// destruction of the `Entry` value, see [`into_mut`].
///
/// [`into_mut`]: #method.into_mut
///
/// # Examples
///
/// ```
@ -2261,10 +2266,14 @@ impl<'a, K, V> OccupiedEntry<'a, K, V> {
///
/// assert_eq!(map["poneyland"], 12);
/// if let Entry::Occupied(mut o) = map.entry("poneyland") {
/// *o.get_mut() += 10;
/// *o.get_mut() += 10;
/// assert_eq!(*o.get(), 22);
///
/// // We can use the same Entry multiple times.
/// *o.get_mut() += 2;
/// }
///
/// assert_eq!(map["poneyland"], 22);
/// assert_eq!(map["poneyland"], 24);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn get_mut(&mut self) -> &mut V {
@ -2274,6 +2283,10 @@ impl<'a, K, V> OccupiedEntry<'a, K, V> {
/// Converts the OccupiedEntry into a mutable reference to the value in the entry
/// with a lifetime bound to the map itself.
///
/// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
///
/// [`get_mut`]: #method.get_mut
///
/// # Examples
///
/// ```