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author | Alex Crichton <alex@alexcrichton.com> | 2014-12-09 12:37:23 -0800 |
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committer | Alex Crichton <alex@alexcrichton.com> | 2015-01-07 12:18:08 -0800 |
commit | 511f0b8a3de5a166fc96aba5170782c9abf92101 (patch) | |
tree | 89f96ae820351742b56d424decfa393a1660e049 /src/libserialize/collection_impls.rs | |
parent | 9e4e524e0eb17c8f463e731f23b544003e8709c6 (diff) | |
download | rust-511f0b8a3de5a166fc96aba5170782c9abf92101.tar.gz |
std: Stabilize the std::hash module
This commit aims to prepare the `std::hash` module for alpha by formalizing its
current interface whileholding off on adding `#[stable]` to the new APIs. The
current usage with the `HashMap` and `HashSet` types is also reconciled by
separating out composable parts of the design. The primary goal of this slight
redesign is to separate the concepts of a hasher's state from a hashing
algorithm itself.
The primary change of this commit is to separate the `Hasher` trait into a
`Hasher` and a `HashState` trait. Conceptually the old `Hasher` trait was
actually just a factory for various states, but hashing had very little control
over how these states were used. Additionally the old `Hasher` trait was
actually fairly unrelated to hashing.
This commit redesigns the existing `Hasher` trait to match what the notion of a
`Hasher` normally implies with the following definition:
trait Hasher {
type Output;
fn reset(&mut self);
fn finish(&self) -> Output;
}
This `Hasher` trait emphasizes that hashing algorithms may produce outputs other
than a `u64`, so the output type is made generic. Other than that, however, very
little is assumed about a particular hasher. It is left up to implementors to
provide specific methods or trait implementations to feed data into a hasher.
The corresponding `Hash` trait becomes:
trait Hash<H: Hasher> {
fn hash(&self, &mut H);
}
The old default of `SipState` was removed from this trait as it's not something
that we're willing to stabilize until the end of time, but the type parameter is
always required to implement `Hasher`. Note that the type parameter `H` remains
on the trait to enable multidispatch for specialization of hashing for
particular hashers.
Note that `Writer` is not mentioned in either of `Hash` or `Hasher`, it is
simply used as part `derive` and the implementations for all primitive types.
With these definitions, the old `Hasher` trait is realized as a new `HashState`
trait in the `collections::hash_state` module as an unstable addition for
now. The current definition looks like:
trait HashState {
type Hasher: Hasher;
fn hasher(&self) -> Hasher;
}
The purpose of this trait is to emphasize that the one piece of functionality
for implementors is that new instances of `Hasher` can be created. This
conceptually represents the two keys from which more instances of a
`SipHasher` can be created, and a `HashState` is what's stored in a
`HashMap`, not a `Hasher`.
Implementors of custom hash algorithms should implement the `Hasher` trait, and
only hash algorithms intended for use in hash maps need to implement or worry
about the `HashState` trait.
The entire module and `HashState` infrastructure remains `#[unstable]` due to it
being recently redesigned, but some other stability decision made for the
`std::hash` module are:
* The `Writer` trait remains `#[experimental]` as it's intended to be replaced
with an `io::Writer` (more details soon).
* The top-level `hash` function is `#[unstable]` as it is intended to be generic
over the hashing algorithm instead of hardwired to `SipHasher`
* The inner `sip` module is now private as its one export, `SipHasher` is
reexported in the `hash` module.
And finally, a few changes were made to the default parameters on `HashMap`.
* The `RandomSipHasher` default type parameter was renamed to `RandomState`.
This renaming emphasizes that it is not a hasher, but rather just state to
generate hashers. It also moves away from the name "sip" as it may not always
be implemented as `SipHasher`. This type lives in the
`std::collections::hash_map` module as `#[unstable]`
* The associated `Hasher` type of `RandomState` is creatively called...
`Hasher`! This concrete structure lives next to `RandomState` as an
implemenation of the "default hashing algorithm" used for a `HashMap`. Under
the hood this is currently implemented as `SipHasher`, but it draws an
explicit interface for now and allows us to modify the implementation over
time if necessary.
There are many breaking changes outlined above, and as a result this commit is
a:
[breaking-change]
Diffstat (limited to 'src/libserialize/collection_impls.rs')
-rw-r--r-- | src/libserialize/collection_impls.rs | 60 |
1 files changed, 29 insertions, 31 deletions
diff --git a/src/libserialize/collection_impls.rs b/src/libserialize/collection_impls.rs index d89a4754d2e..42498328ff6 100644 --- a/src/libserialize/collection_impls.rs +++ b/src/libserialize/collection_impls.rs @@ -13,6 +13,7 @@ use std::uint; use std::default::Default; use std::hash::{Hash, Hasher}; +use std::collections::hash_state::HashState; use {Decodable, Encodable, Decoder, Encoder}; use std::collections::{DList, RingBuf, BTreeMap, BTreeSet, HashMap, HashSet, VecMap}; @@ -156,13 +157,12 @@ impl< } } -#[old_impl_check] -impl< - K: Encodable + Hash<X> + Eq, - V: Encodable, - X, - H: Hasher<X> -> Encodable for HashMap<K, V, H> { +impl<K, V, S> Encodable for HashMap<K, V, S> + where K: Encodable + Hash< <S as HashState>::Hasher> + Eq, + V: Encodable, + S: HashState, + <S as HashState>::Hasher: Hasher<Output=u64> +{ fn encode<S: Encoder>(&self, e: &mut S) -> Result<(), S::Error> { e.emit_map(self.len(), |e| { let mut i = 0; @@ -176,17 +176,16 @@ impl< } } -#[old_impl_check] -impl< - K: Decodable + Hash<S> + Eq, - V: Decodable, - S, - H: Hasher<S> + Default -> Decodable for HashMap<K, V, H> { - fn decode<D: Decoder>(d: &mut D) -> Result<HashMap<K, V, H>, D::Error> { +impl<K, V, S> Decodable for HashMap<K, V, S> + where K: Decodable + Hash< <S as HashState>::Hasher> + Eq, + V: Decodable, + S: HashState + Default, + <S as HashState>::Hasher: Hasher<Output=u64> +{ + fn decode<D: Decoder>(d: &mut D) -> Result<HashMap<K, V, S>, D::Error> { d.read_map(|d, len| { - let hasher = Default::default(); - let mut map = HashMap::with_capacity_and_hasher(len, hasher); + let state = Default::default(); + let mut map = HashMap::with_capacity_and_hash_state(len, state); for i in range(0u, len) { let key = try!(d.read_map_elt_key(i, |d| Decodable::decode(d))); let val = try!(d.read_map_elt_val(i, |d| Decodable::decode(d))); @@ -197,12 +196,11 @@ impl< } } -#[old_impl_check] -impl< - T: Encodable + Hash<X> + Eq, - X, - H: Hasher<X> -> Encodable for HashSet<T, H> { +impl<T, S> Encodable for HashSet<T, S> + where T: Encodable + Hash< <S as HashState>::Hasher> + Eq, + S: HashState, + <S as HashState>::Hasher: Hasher<Output=u64> +{ fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> { s.emit_seq(self.len(), |s| { let mut i = 0; @@ -215,15 +213,15 @@ impl< } } -#[old_impl_check] -impl< - T: Decodable + Hash<S> + Eq, - S, - H: Hasher<S> + Default -> Decodable for HashSet<T, H> { - fn decode<D: Decoder>(d: &mut D) -> Result<HashSet<T, H>, D::Error> { +impl<T, S> Decodable for HashSet<T, S> + where T: Decodable + Hash< <S as HashState>::Hasher> + Eq, + S: HashState + Default, + <S as HashState>::Hasher: Hasher<Output=u64> +{ + fn decode<D: Decoder>(d: &mut D) -> Result<HashSet<T, S>, D::Error> { d.read_seq(|d, len| { - let mut set = HashSet::with_capacity_and_hasher(len, Default::default()); + let state = Default::default(); + let mut set = HashSet::with_capacity_and_hash_state(len, state); for i in range(0u, len) { set.insert(try!(d.read_seq_elt(i, |d| Decodable::decode(d)))); } |