Rollup merge of #23559 - aturon:future-proof-map-index, r=Gankro

 This commit removes the `IndexMut` impls on `HashMap` and `BTreeMap`, in
order to future-proof the API against the eventual inclusion of an
`IndexSet` trait.

Ideally, we would eventually be able to support:

```rust
map[owned_key] = val;
map[borrowed_key].mutating_method(arguments);
&mut map[borrowed_key];
```

but to keep the design space as unconstrained as possible, we do not
currently want to support `IndexMut`, in case some other strategy will
eventually be needed.

Code currently using mutating index notation can use `get_mut` instead.

[breaking-change]

Closes #23448

r? @Gankro

1 files changed, 1 insertions, 13 deletions

diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 60b1738d2c9..9139e182ce4 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -23,7 +23,7 @@ use hash::{Hash, SipHasher};
 use iter::{self, Iterator, ExactSizeIterator, IntoIterator, IteratorExt, FromIterator, Extend, Map};
 use marker::Sized;
 use mem::{self, replace};
-use ops::{Deref, FnMut, Index, IndexMut};
+use ops::{Deref, FnMut, Index};
 use option::Option::{self, Some, None};
 use rand::{self, Rng};
 use result::Result::{self, Ok, Err};
@@ -1258,18 +1258,6 @@ impl<K, Q: ?Sized, V, S> Index<Q> for HashMap<K, V, S>
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<K, V, S, Q: ?Sized> IndexMut<Q> for HashMap<K, V, S>
-    where K: Eq + Hash + Borrow<Q>,
-          Q: Eq + Hash,
-          S: HashState,
-{
-    #[inline]
-    fn index_mut<'a>(&'a mut self, index: &Q) -> &'a mut V {
-        self.get_mut(index).expect("no entry found for key")
-    }
-}
-
 /// HashMap iterator.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Iter<'a, K: 'a, V: 'a> {