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