1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![unstable(feature = "hashmap_hasher", reason = "hasher stuff is unclear",
19 /// A trait representing stateful hashes which can be used to hash keys in a
22 /// A HashState is used as a factory for instances of `Hasher` which a `HashMap`
23 /// can then use to hash keys independently. A `HashMap` by default uses a state
24 /// which will create instances of a `SipHasher`, but a custom state factory can
25 /// be provided to the `with_hash_state` function.
27 /// If a hashing algorithm has no initial state, then the `Hasher` type for that
28 /// algorithm can implement the `Default` trait and create hash maps with the
29 /// `DefaultState` structure. This state is 0-sized and will simply delegate
30 /// to `Default` when asked to create a hasher.
32 /// Type of the hasher that will be created.
33 type Hasher: hash::Hasher;
35 /// Creates a new hasher based on the given state of this object.
36 fn hasher(&self) -> Self::Hasher;
39 /// A structure which is a factory for instances of `Hasher` which implement the
42 /// This struct is 0-sized and does not need construction.
43 pub struct DefaultState<H>(marker::PhantomData<H>);
45 impl<H: Default + hash::Hasher> HashState for DefaultState<H> {
47 fn hasher(&self) -> H { Default::default() }
50 impl<H> Clone for DefaultState<H> {
51 fn clone(&self) -> DefaultState<H> { DefaultState(marker::PhantomData) }
54 impl<H> Default for DefaultState<H> {
55 fn default() -> DefaultState<H> { DefaultState(marker::PhantomData) }