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")]
18 /// A trait representing stateful hashes which can be used to hash keys in a
21 /// A HashState is used as a factory for instances of `Hasher` which a `HashMap`
22 /// can then use to hash keys independently. A `HashMap` by default uses a state
23 /// which will create instances of a `SipHasher`, but a custom state factory can
24 /// be provided to the `with_hash_state` function.
26 /// If a hashing algorithm has no initial state, then the `Hasher` type for that
27 /// algorithm can implement the `Default` trait and create hash maps with the
28 /// `DefaultState` structure. This state is 0-sized and will simply delegate
29 /// to `Default` when asked to create a hasher.
31 /// Type of the hasher that will be created.
32 type Hasher: hash::Hasher;
34 /// Creates a new hasher based on the given state of this object.
35 fn hasher(&self) -> Self::Hasher;
38 /// A structure which is a factory for instances of `Hasher` which implement the
41 /// This struct has is 0-sized and does not need construction.
42 pub struct DefaultState<H>(marker::PhantomData<H>);
44 impl<H: Default + hash::Hasher> HashState for DefaultState<H> {
46 fn hasher(&self) -> H { Default::default() }
49 impl<H> Clone for DefaultState<H> {
50 fn clone(&self) -> DefaultState<H> { DefaultState(marker::PhantomData) }
53 impl<H> Default for DefaultState<H> {
54 fn default() -> DefaultState<H> { DefaultState(marker::PhantomData) }