713 lines
21 KiB
Rust
713 lines
21 KiB
Rust
//! Generic hashing support.
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//!
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//! This module provides a generic way to compute the hash of a value. The
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//! simplest way to make a type hashable is to use `#[derive(Hash)]`:
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//!
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//! # Examples
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//!
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//! ```rust
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//! use std::collections::hash_map::DefaultHasher;
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//! use std::hash::{Hash, Hasher};
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//!
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//! #[derive(Hash)]
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//! struct Person {
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//! id: u32,
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//! name: String,
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//! phone: u64,
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//! }
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//!
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//! let person1 = Person {
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//! id: 5,
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//! name: "Janet".to_string(),
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//! phone: 555_666_7777,
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//! };
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//! let person2 = Person {
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//! id: 5,
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//! name: "Bob".to_string(),
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//! phone: 555_666_7777,
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//! };
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//!
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//! assert!(calculate_hash(&person1) != calculate_hash(&person2));
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//!
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//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
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//! let mut s = DefaultHasher::new();
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//! t.hash(&mut s);
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//! s.finish()
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//! }
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//! ```
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//!
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//! If you need more control over how a value is hashed, you need to implement
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//! the [`Hash`] trait:
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//!
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//! ```rust
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//! use std::collections::hash_map::DefaultHasher;
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//! use std::hash::{Hash, Hasher};
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//!
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//! struct Person {
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//! id: u32,
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//! # #[allow(dead_code)]
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//! name: String,
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//! phone: u64,
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//! }
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//!
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//! impl Hash for Person {
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//! fn hash<H: Hasher>(&self, state: &mut H) {
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//! self.id.hash(state);
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//! self.phone.hash(state);
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//! }
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//! }
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//!
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//! let person1 = Person {
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//! id: 5,
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//! name: "Janet".to_string(),
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//! phone: 555_666_7777,
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//! };
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//! let person2 = Person {
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//! id: 5,
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//! name: "Bob".to_string(),
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//! phone: 555_666_7777,
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//! };
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//!
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//! assert_eq!(calculate_hash(&person1), calculate_hash(&person2));
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//!
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//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
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//! let mut s = DefaultHasher::new();
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//! t.hash(&mut s);
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//! s.finish()
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//! }
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//! ```
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#![stable(feature = "rust1", since = "1.0.0")]
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use crate::fmt;
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use crate::marker;
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#[stable(feature = "rust1", since = "1.0.0")]
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#[allow(deprecated)]
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pub use self::sip::SipHasher;
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#[unstable(feature = "hashmap_internals", issue = "none")]
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#[allow(deprecated)]
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#[doc(hidden)]
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pub use self::sip::SipHasher13;
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mod sip;
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/// A hashable type.
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///
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/// Types implementing `Hash` are able to be [`hash`]ed with an instance of
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/// [`Hasher`].
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///
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/// ## Implementing `Hash`
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///
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/// You can derive `Hash` with `#[derive(Hash)]` if all fields implement `Hash`.
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/// The resulting hash will be the combination of the values from calling
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/// [`hash`] on each field.
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///
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/// ```
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/// #[derive(Hash)]
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/// struct Rustacean {
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/// name: String,
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/// country: String,
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/// }
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/// ```
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///
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/// If you need more control over how a value is hashed, you can of course
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/// implement the `Hash` trait yourself:
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///
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/// ```
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/// use std::hash::{Hash, Hasher};
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///
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/// struct Person {
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/// id: u32,
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/// name: String,
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/// phone: u64,
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/// }
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///
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/// impl Hash for Person {
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/// fn hash<H: Hasher>(&self, state: &mut H) {
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/// self.id.hash(state);
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/// self.phone.hash(state);
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/// }
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/// }
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/// ```
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///
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/// ## `Hash` and `Eq`
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///
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/// When implementing both `Hash` and [`Eq`], it is important that the following
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/// property holds:
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///
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/// ```text
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/// k1 == k2 -> hash(k1) == hash(k2)
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/// ```
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///
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/// In other words, if two keys are equal, their hashes must also be equal.
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/// [`HashMap`] and [`HashSet`] both rely on this behavior.
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///
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/// Thankfully, you won't need to worry about upholding this property when
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/// deriving both [`Eq`] and `Hash` with `#[derive(PartialEq, Eq, Hash)]`.
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///
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/// [`HashMap`]: ../../std/collections/struct.HashMap.html
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/// [`HashSet`]: ../../std/collections/struct.HashSet.html
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/// [`hash`]: Hash::hash
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Hash {
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/// Feeds this value into the given [`Hasher`].
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::DefaultHasher;
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/// use std::hash::{Hash, Hasher};
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///
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/// let mut hasher = DefaultHasher::new();
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/// 7920.hash(&mut hasher);
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/// println!("Hash is {:x}!", hasher.finish());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn hash<H: Hasher>(&self, state: &mut H);
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/// Feeds a slice of this type into the given [`Hasher`].
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::DefaultHasher;
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/// use std::hash::{Hash, Hasher};
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///
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/// let mut hasher = DefaultHasher::new();
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/// let numbers = [6, 28, 496, 8128];
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/// Hash::hash_slice(&numbers, &mut hasher);
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/// println!("Hash is {:x}!", hasher.finish());
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/// ```
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#[stable(feature = "hash_slice", since = "1.3.0")]
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fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)
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where
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Self: Sized,
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{
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for piece in data {
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piece.hash(state);
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}
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}
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}
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// Separate module to reexport the macro `Hash` from prelude without the trait `Hash`.
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pub(crate) mod macros {
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/// Derive macro generating an impl of the trait `Hash`.
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#[rustc_builtin_macro]
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#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
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#[allow_internal_unstable(core_intrinsics)]
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pub macro Hash($item:item) {
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/* compiler built-in */
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}
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}
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#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
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#[doc(inline)]
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pub use macros::Hash;
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/// A trait for hashing an arbitrary stream of bytes.
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///
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/// Instances of `Hasher` usually represent state that is changed while hashing
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/// data.
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///
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/// `Hasher` provides a fairly basic interface for retrieving the generated hash
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/// (with [`finish`]), and writing integers as well as slices of bytes into an
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/// instance (with [`write`] and [`write_u8`] etc.). Most of the time, `Hasher`
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/// instances are used in conjunction with the [`Hash`] trait.
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::DefaultHasher;
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/// use std::hash::Hasher;
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///
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/// let mut hasher = DefaultHasher::new();
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///
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/// hasher.write_u32(1989);
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/// hasher.write_u8(11);
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/// hasher.write_u8(9);
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/// hasher.write(b"Huh?");
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///
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/// println!("Hash is {:x}!", hasher.finish());
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/// ```
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///
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/// [`finish`]: Hasher::finish
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/// [`write`]: Hasher::write
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/// [`write_u8`]: Hasher::write_u8
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Hasher {
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/// Returns the hash value for the values written so far.
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///
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/// Despite its name, the method does not reset the hasher’s internal
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/// state. Additional [`write`]s will continue from the current value.
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/// If you need to start a fresh hash value, you will have to create
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/// a new hasher.
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::DefaultHasher;
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/// use std::hash::Hasher;
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///
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/// let mut hasher = DefaultHasher::new();
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/// hasher.write(b"Cool!");
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///
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/// println!("Hash is {:x}!", hasher.finish());
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/// ```
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///
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/// [`write`]: Hasher::write
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#[stable(feature = "rust1", since = "1.0.0")]
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fn finish(&self) -> u64;
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/// Writes some data into this `Hasher`.
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::DefaultHasher;
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/// use std::hash::Hasher;
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///
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/// let mut hasher = DefaultHasher::new();
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/// let data = [0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef];
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///
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/// hasher.write(&data);
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///
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/// println!("Hash is {:x}!", hasher.finish());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn write(&mut self, bytes: &[u8]);
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/// Writes a single `u8` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_u8(&mut self, i: u8) {
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self.write(&[i])
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}
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/// Writes a single `u16` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_u16(&mut self, i: u16) {
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self.write(&i.to_ne_bytes())
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}
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/// Writes a single `u32` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_u32(&mut self, i: u32) {
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self.write(&i.to_ne_bytes())
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}
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/// Writes a single `u64` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_u64(&mut self, i: u64) {
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self.write(&i.to_ne_bytes())
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}
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/// Writes a single `u128` into this hasher.
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#[inline]
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#[stable(feature = "i128", since = "1.26.0")]
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fn write_u128(&mut self, i: u128) {
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self.write(&i.to_ne_bytes())
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}
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/// Writes a single `usize` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_usize(&mut self, i: usize) {
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self.write(&i.to_ne_bytes())
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}
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/// Writes a single `i8` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_i8(&mut self, i: i8) {
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self.write_u8(i as u8)
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}
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/// Writes a single `i16` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_i16(&mut self, i: i16) {
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self.write_u16(i as u16)
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}
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/// Writes a single `i32` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_i32(&mut self, i: i32) {
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self.write_u32(i as u32)
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}
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/// Writes a single `i64` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_i64(&mut self, i: i64) {
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self.write_u64(i as u64)
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}
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/// Writes a single `i128` into this hasher.
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#[inline]
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#[stable(feature = "i128", since = "1.26.0")]
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fn write_i128(&mut self, i: i128) {
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self.write_u128(i as u128)
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}
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/// Writes a single `isize` into this hasher.
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#[inline]
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#[stable(feature = "hasher_write", since = "1.3.0")]
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fn write_isize(&mut self, i: isize) {
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self.write_usize(i as usize)
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}
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}
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#[stable(feature = "indirect_hasher_impl", since = "1.22.0")]
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impl<H: Hasher + ?Sized> Hasher for &mut H {
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fn finish(&self) -> u64 {
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(**self).finish()
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}
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fn write(&mut self, bytes: &[u8]) {
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(**self).write(bytes)
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}
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fn write_u8(&mut self, i: u8) {
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(**self).write_u8(i)
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}
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fn write_u16(&mut self, i: u16) {
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(**self).write_u16(i)
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}
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fn write_u32(&mut self, i: u32) {
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(**self).write_u32(i)
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}
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fn write_u64(&mut self, i: u64) {
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(**self).write_u64(i)
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}
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fn write_u128(&mut self, i: u128) {
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(**self).write_u128(i)
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}
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fn write_usize(&mut self, i: usize) {
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(**self).write_usize(i)
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}
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fn write_i8(&mut self, i: i8) {
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(**self).write_i8(i)
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}
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fn write_i16(&mut self, i: i16) {
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(**self).write_i16(i)
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}
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fn write_i32(&mut self, i: i32) {
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(**self).write_i32(i)
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}
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fn write_i64(&mut self, i: i64) {
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(**self).write_i64(i)
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}
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fn write_i128(&mut self, i: i128) {
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(**self).write_i128(i)
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}
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fn write_isize(&mut self, i: isize) {
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(**self).write_isize(i)
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}
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}
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/// A trait for creating instances of [`Hasher`].
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///
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/// A `BuildHasher` is typically used (e.g., by [`HashMap`]) to create
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/// [`Hasher`]s for each key such that they are hashed independently of one
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/// another, since [`Hasher`]s contain state.
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///
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/// For each instance of `BuildHasher`, the [`Hasher`]s created by
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/// [`build_hasher`] should be identical. That is, if the same stream of bytes
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/// is fed into each hasher, the same output will also be generated.
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::RandomState;
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/// use std::hash::{BuildHasher, Hasher};
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///
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/// let s = RandomState::new();
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/// let mut hasher_1 = s.build_hasher();
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/// let mut hasher_2 = s.build_hasher();
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///
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/// hasher_1.write_u32(8128);
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/// hasher_2.write_u32(8128);
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///
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/// assert_eq!(hasher_1.finish(), hasher_2.finish());
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/// ```
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///
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/// [`build_hasher`]: BuildHasher::build_hasher
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/// [`HashMap`]: ../../std/collections/struct.HashMap.html
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#[stable(since = "1.7.0", feature = "build_hasher")]
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pub trait BuildHasher {
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/// Type of the hasher that will be created.
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#[stable(since = "1.7.0", feature = "build_hasher")]
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type Hasher: Hasher;
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/// Creates a new hasher.
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///
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/// Each call to `build_hasher` on the same instance should produce identical
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/// [`Hasher`]s.
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///
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/// # Examples
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///
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/// ```
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/// use std::collections::hash_map::RandomState;
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/// use std::hash::BuildHasher;
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///
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/// let s = RandomState::new();
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/// let new_s = s.build_hasher();
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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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}
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/// Used to create a default [`BuildHasher`] instance for types that implement
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/// [`Hasher`] and [`Default`].
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///
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/// `BuildHasherDefault<H>` can be used when a type `H` implements [`Hasher`] and
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/// [`Default`], and you need a corresponding [`BuildHasher`] instance, but none is
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/// defined.
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///
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/// Any `BuildHasherDefault` is [zero-sized]. It can be created with
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/// [`default`][method.default]. When using `BuildHasherDefault` with [`HashMap`] or
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/// [`HashSet`], this doesn't need to be done, since they implement appropriate
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/// [`Default`] instances themselves.
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///
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/// # Examples
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///
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/// Using `BuildHasherDefault` to specify a custom [`BuildHasher`] for
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/// [`HashMap`]:
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///
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/// ```
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/// use std::collections::HashMap;
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/// use std::hash::{BuildHasherDefault, Hasher};
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///
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/// #[derive(Default)]
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/// struct MyHasher;
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///
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/// impl Hasher for MyHasher {
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/// fn write(&mut self, bytes: &[u8]) {
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/// // Your hashing algorithm goes here!
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/// unimplemented!()
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/// }
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///
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/// fn finish(&self) -> u64 {
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/// // Your hashing algorithm goes here!
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/// unimplemented!()
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/// }
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/// }
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///
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/// type MyBuildHasher = BuildHasherDefault<MyHasher>;
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///
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/// let hash_map = HashMap::<u32, u32, MyBuildHasher>::default();
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/// ```
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///
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/// [method.default]: BuildHasherDefault::default
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/// [`HashMap`]: ../../std/collections/struct.HashMap.html
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/// [`HashSet`]: ../../std/collections/struct.HashSet.html
|
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/// [zero-sized]: https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts
|
||
#[stable(since = "1.7.0", feature = "build_hasher")]
|
||
pub struct BuildHasherDefault<H>(marker::PhantomData<H>);
|
||
|
||
#[stable(since = "1.9.0", feature = "core_impl_debug")]
|
||
impl<H> fmt::Debug for BuildHasherDefault<H> {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
f.pad("BuildHasherDefault")
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.7.0", feature = "build_hasher")]
|
||
impl<H: Default + Hasher> BuildHasher for BuildHasherDefault<H> {
|
||
type Hasher = H;
|
||
|
||
fn build_hasher(&self) -> H {
|
||
H::default()
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.7.0", feature = "build_hasher")]
|
||
impl<H> Clone for BuildHasherDefault<H> {
|
||
fn clone(&self) -> BuildHasherDefault<H> {
|
||
BuildHasherDefault(marker::PhantomData)
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.7.0", feature = "build_hasher")]
|
||
impl<H> Default for BuildHasherDefault<H> {
|
||
fn default() -> BuildHasherDefault<H> {
|
||
BuildHasherDefault(marker::PhantomData)
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.29.0", feature = "build_hasher_eq")]
|
||
impl<H> PartialEq for BuildHasherDefault<H> {
|
||
fn eq(&self, _other: &BuildHasherDefault<H>) -> bool {
|
||
true
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.29.0", feature = "build_hasher_eq")]
|
||
impl<H> Eq for BuildHasherDefault<H> {}
|
||
|
||
mod impls {
|
||
use crate::mem;
|
||
use crate::slice;
|
||
|
||
use super::*;
|
||
|
||
macro_rules! impl_write {
|
||
($(($ty:ident, $meth:ident),)*) => {$(
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl Hash for $ty {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
state.$meth(*self)
|
||
}
|
||
|
||
fn hash_slice<H: Hasher>(data: &[$ty], state: &mut H) {
|
||
let newlen = data.len() * mem::size_of::<$ty>();
|
||
let ptr = data.as_ptr() as *const u8;
|
||
// SAFETY: `ptr` is valid and aligned, as this macro is only used
|
||
// for numeric primitives which have no padding. The new slice only
|
||
// spans across `data` and is never mutated, and its total size is the
|
||
// same as the original `data` so it can't be over `isize::MAX`.
|
||
state.write(unsafe { slice::from_raw_parts(ptr, newlen) })
|
||
}
|
||
}
|
||
)*}
|
||
}
|
||
|
||
impl_write! {
|
||
(u8, write_u8),
|
||
(u16, write_u16),
|
||
(u32, write_u32),
|
||
(u64, write_u64),
|
||
(usize, write_usize),
|
||
(i8, write_i8),
|
||
(i16, write_i16),
|
||
(i32, write_i32),
|
||
(i64, write_i64),
|
||
(isize, write_isize),
|
||
(u128, write_u128),
|
||
(i128, write_i128),
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl Hash for bool {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
state.write_u8(*self as u8)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl Hash for char {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
state.write_u32(*self as u32)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl Hash for str {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
state.write(self.as_bytes());
|
||
state.write_u8(0xff)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "never_hash", since = "1.29.0")]
|
||
impl Hash for ! {
|
||
fn hash<H: Hasher>(&self, _: &mut H) {
|
||
*self
|
||
}
|
||
}
|
||
|
||
macro_rules! impl_hash_tuple {
|
||
() => (
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl Hash for () {
|
||
fn hash<H: Hasher>(&self, _state: &mut H) {}
|
||
}
|
||
);
|
||
|
||
( $($name:ident)+) => (
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<$($name: Hash),+> Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
|
||
#[allow(non_snake_case)]
|
||
fn hash<S: Hasher>(&self, state: &mut S) {
|
||
let ($(ref $name,)+) = *self;
|
||
$($name.hash(state);)+
|
||
}
|
||
}
|
||
);
|
||
}
|
||
|
||
macro_rules! last_type {
|
||
($a:ident,) => { $a };
|
||
($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
|
||
}
|
||
|
||
impl_hash_tuple! {}
|
||
impl_hash_tuple! { A }
|
||
impl_hash_tuple! { A B }
|
||
impl_hash_tuple! { A B C }
|
||
impl_hash_tuple! { A B C D }
|
||
impl_hash_tuple! { A B C D E }
|
||
impl_hash_tuple! { A B C D E F }
|
||
impl_hash_tuple! { A B C D E F G }
|
||
impl_hash_tuple! { A B C D E F G H }
|
||
impl_hash_tuple! { A B C D E F G H I }
|
||
impl_hash_tuple! { A B C D E F G H I J }
|
||
impl_hash_tuple! { A B C D E F G H I J K }
|
||
impl_hash_tuple! { A B C D E F G H I J K L }
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: Hash> Hash for [T] {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
self.len().hash(state);
|
||
Hash::hash_slice(self, state)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Hash> Hash for &T {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
(**self).hash(state);
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Hash> Hash for &mut T {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
(**self).hash(state);
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Hash for *const T {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
if mem::size_of::<Self>() == mem::size_of::<usize>() {
|
||
// Thin pointer
|
||
state.write_usize(*self as *const () as usize);
|
||
} else {
|
||
// Fat pointer
|
||
// SAFETY: we are accessing the memory occupied by `self`
|
||
// which is guaranteed to be valid.
|
||
// This assumes a fat pointer can be represented by a `(usize, usize)`,
|
||
// which is safe to do in `std` because it is shipped and kept in sync
|
||
// with the implementation of fat pointers in `rustc`.
|
||
let (a, b) = unsafe { *(self as *const Self as *const (usize, usize)) };
|
||
state.write_usize(a);
|
||
state.write_usize(b);
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Hash for *mut T {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
if mem::size_of::<Self>() == mem::size_of::<usize>() {
|
||
// Thin pointer
|
||
state.write_usize(*self as *const () as usize);
|
||
} else {
|
||
// Fat pointer
|
||
// SAFETY: we are accessing the memory occupied by `self`
|
||
// which is guaranteed to be valid.
|
||
// This assumes a fat pointer can be represented by a `(usize, usize)`,
|
||
// which is safe to do in `std` because it is shipped and kept in sync
|
||
// with the implementation of fat pointers in `rustc`.
|
||
let (a, b) = unsafe { *(self as *const Self as *const (usize, usize)) };
|
||
state.write_usize(a);
|
||
state.write_usize(b);
|
||
}
|
||
}
|
||
}
|
||
}
|