impl Hasher for {&mut Hasher, Box<Hasher>}

2 files changed, 56 insertions, 0 deletions

diff --git a/src/libcore/hash/mod.rs b/src/libcore/hash/mod.rs
index a8b84203d6a..bc1b911cd78 100644
--- a/src/libcore/hash/mod.rs
+++ b/src/libcore/hash/mod.rs
@@ -359,6 +359,52 @@ pub trait Hasher {
     }
 }
 
+#[stable(feature = "indirect_hasher_impl", since = "1.22.0")]
+impl<'a, H: Hasher + ?Sized> Hasher for &'a mut H {
+    fn finish(&self) -> u64 {
+        (**self).finish()
+    }
+    fn write(&mut self, bytes: &[u8]) {
+        (**self).write(bytes)
+    }
+    fn write_u8(&mut self, i: u8) {
+        (**self).write_u8(i)
+    }
+    fn write_u16(&mut self, i: u16) {
+        (**self).write_u16(i)
+    }
+    fn write_u32(&mut self, i: u32) {
+        (**self).write_u32(i)
+    }
+    fn write_u64(&mut self, i: u64) {
+        (**self).write_u64(i)
+    }
+    fn write_u128(&mut self, i: u128) {
+        (**self).write_u128(i)
+    }
+    fn write_usize(&mut self, i: usize) {
+        (**self).write_usize(i)
+    }
+    fn write_i8(&mut self, i: i8) {
+        (**self).write_i8(i)
+    }
+    fn write_i16(&mut self, i: i16) {
+        (**self).write_i16(i)
+    }
+    fn write_i32(&mut self, i: i32) {
+        (**self).write_i32(i)
+    }
+    fn write_i64(&mut self, i: i64) {
+        (**self).write_i64(i)
+    }
+    fn write_i128(&mut self, i: i128) {
+        (**self).write_i128(i)
+    }
+    fn write_isize(&mut self, i: isize) {
+        (**self).write_isize(i)
+    }
+}
+
 /// A trait for creating instances of [`Hasher`].
 ///
 /// A `BuildHasher` is typically used (e.g. by [`HashMap`]) to create
diff --git a/src/libcore/tests/hash/mod.rs b/src/libcore/tests/hash/mod.rs
index 53ac17c052f..49e41f02428 100644
--- a/src/libcore/tests/hash/mod.rs
+++ b/src/libcore/tests/hash/mod.rs
@@ -109,3 +109,13 @@ fn test_custom_state() {
 
     assert_eq!(hash(&Custom { hash: 5 }), 5);
 }
+
+#[test]
+fn test_indirect_hasher() {
+    let mut hasher = MyHasher { hash: 0 };
+    {
+        let mut indirect_hasher: &mut Hasher = &mut hasher;
+        5u32.hash(&mut indirect_hasher);
+    }
+    assert_eq!(hasher.hash, 5);
+}