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Add BuildHasher::hash_of
as unstable
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@ -481,6 +481,50 @@ pub trait BuildHasher {
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/// ```
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#[stable(since = "1.7.0", feature = "build_hasher")]
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fn build_hasher(&self) -> Self::Hasher;
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/// Calculates the hash of a single value.
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///
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/// This is intended as a convenience for code which *consumes* hashes, such
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/// as the implementation of a hash table or in unit tests that check
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/// whether a custom [`Hash`] implementation behaves as expected.
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///
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/// This must not be used in any code which *creates* hashes, such as in an
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/// implementation of [`Hash`]. The way to create a combined hash of
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/// multiple values is to call [`Hash::hash`] multiple times using the same
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/// [`Hasher`], not to call this method repeatedly and combine the results.
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///
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/// # Example
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///
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/// ```
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/// #![feature(build_hasher_simple_hash_of)]
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///
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/// use std::cmp::{max, min};
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/// use std::hash::{BuildHasher, Hash, Hasher};
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/// struct OrderAmbivalentPair<T: Ord>(T, T);
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/// impl<T: Ord + Hash> Hash for OrderAmbivalentPair<T> {
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/// fn hash<H: Hasher>(&self, hasher: &mut H) {
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/// min(&self.0, &self.1).hash(hasher);
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/// max(&self.0, &self.1).hash(hasher);
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/// }
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/// }
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///
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/// // Then later, in a `#[test]` for the type...
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/// let bh = std::collections::hash_map::RandomState::new();
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/// assert_eq!(
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/// bh.hash_of(OrderAmbivalentPair(1, 2)),
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/// bh.hash_of(OrderAmbivalentPair(2, 1))
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/// );
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/// assert_eq!(
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/// bh.hash_of(OrderAmbivalentPair(10, 2)),
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/// bh.hash_of(&OrderAmbivalentPair(2, 10))
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/// );
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/// ```
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#[unstable(feature = "build_hasher_simple_hash_of", issue = "88888888")]
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fn hash_of<T: Hash>(&self, x: T) -> u64 {
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let mut hasher = self.build_hasher();
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x.hash(&mut hasher);
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hasher.finish()
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}
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}
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/// Used to create a default [`BuildHasher`] instance for types that implement
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