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//! Generic hashing support. //! //! This module provides a generic way to compute the hash of a value. The //! simplest way to make a type hashable is to use `#[derive(Hash)]`: //! //! # Examples //! //! ```rust //! use std::collections::hash_map::DefaultHasher; //! use std::hash::{Hash, Hasher}; //! //! #[derive(Hash)] //! struct Person { //! id: u32, //! name: String, //! phone: u64, //! } //! //! let person1 = Person { //! id: 5, //! name: "Janet".to_string(), //! phone: 555_666_7777, //! }; //! let person2 = Person { //! id: 5, //! name: "Bob".to_string(), //! phone: 555_666_7777, //! }; //! //! assert!(calculate_hash(&person1) != calculate_hash(&person2)); //! //! fn calculate_hash<T: Hash>(t: &T) -> u64 { //! let mut s = DefaultHasher::new(); //! t.hash(&mut s); //! s.finish() //! } //! ``` //! //! If you need more control over how a value is hashed, you need to implement //! the [`Hash`] trait: //! //! [`Hash`]: trait.Hash.html //! //! ```rust //! use std::collections::hash_map::DefaultHasher; //! use std::hash::{Hash, Hasher}; //! //! struct Person { //! id: u32, //! # #[allow(dead_code)] //! name: String, //! phone: u64, //! } //! //! impl Hash for Person { //! fn hash<H: Hasher>(&self, state: &mut H) { //! self.id.hash(state); //! self.phone.hash(state); //! } //! } //! //! let person1 = Person { //! id: 5, //! name: "Janet".to_string(), //! phone: 555_666_7777, //! }; //! let person2 = Person { //! id: 5, //! name: "Bob".to_string(), //! phone: 555_666_7777, //! }; //! //! assert_eq!(calculate_hash(&person1), calculate_hash(&person2)); //! //! fn calculate_hash<T: Hash>(t: &T) -> u64 { //! let mut s = DefaultHasher::new(); //! t.hash(&mut s); //! s.finish() //! } //! ``` #![stable(feature = "rust1", since = "1.0.0")] use crate::fmt; use crate::marker; #[stable(feature = "rust1", since = "1.0.0")] #[allow(deprecated)] pub use self::sip::SipHasher; #[unstable(feature = "hashmap_internals", issue = "0")] #[allow(deprecated)] #[doc(hidden)] pub use self::sip::SipHasher13; mod sip; /// A hashable type. /// /// Types implementing `Hash` are able to be [`hash`]ed with an instance of /// [`Hasher`]. /// /// ## Implementing `Hash` /// /// You can derive `Hash` with `#[derive(Hash)]` if all fields implement `Hash`. /// The resulting hash will be the combination of the values from calling /// [`hash`] on each field. /// /// ``` /// #[derive(Hash)] /// struct Rustacean { /// name: String, /// country: String, /// } /// ``` /// /// If you need more control over how a value is hashed, you can of course /// implement the `Hash` trait yourself: /// /// ``` /// use std::hash::{Hash, Hasher}; /// /// struct Person { /// id: u32, /// name: String, /// phone: u64, /// } /// /// impl Hash for Person { /// fn hash<H: Hasher>(&self, state: &mut H) { /// self.id.hash(state); /// self.phone.hash(state); /// } /// } /// ``` /// /// ## `Hash` and `Eq` /// /// When implementing both `Hash` and [`Eq`], it is important that the following /// property holds: /// /// ```text /// k1 == k2 -> hash(k1) == hash(k2) /// ``` /// /// In other words, if two keys are equal, their hashes must also be equal. /// [`HashMap`] and [`HashSet`] both rely on this behavior. /// /// Thankfully, you won't need to worry about upholding this property when /// deriving both [`Eq`] and `Hash` with `#[derive(PartialEq, Eq, Hash)]`. /// /// [`Eq`]: ../../std/cmp/trait.Eq.html /// [`Hasher`]: trait.Hasher.html /// [`HashMap`]: ../../std/collections/struct.HashMap.html /// [`HashSet`]: ../../std/collections/struct.HashSet.html /// [`hash`]: #tymethod.hash #[stable(feature = "rust1", since = "1.0.0")] pub trait Hash { /// Feeds this value into the given [`Hasher`]. /// /// # Examples /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::{Hash, Hasher}; /// /// let mut hasher = DefaultHasher::new(); /// 7920.hash(&mut hasher); /// println!("Hash is {:x}!", hasher.finish()); /// ``` /// /// [`Hasher`]: trait.Hasher.html #[stable(feature = "rust1", since = "1.0.0")] fn hash<H: Hasher>(&self, state: &mut H); /// Feeds a slice of this type into the given [`Hasher`]. /// /// # Examples /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::{Hash, Hasher}; /// /// let mut hasher = DefaultHasher::new(); /// let numbers = [6, 28, 496, 8128]; /// Hash::hash_slice(&numbers, &mut hasher); /// println!("Hash is {:x}!", hasher.finish()); /// ``` /// /// [`Hasher`]: trait.Hasher.html #[stable(feature = "hash_slice", since = "1.3.0")] fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where Self: Sized { for piece in data { piece.hash(state); } } } /// A trait for hashing an arbitrary stream of bytes. /// /// Instances of `Hasher` usually represent state that is changed while hashing /// data. /// /// `Hasher` provides a fairly basic interface for retrieving the generated hash /// (with [`finish`]), and writing integers as well as slices of bytes into an /// instance (with [`write`] and [`write_u8`] etc.). Most of the time, `Hasher` /// instances are used in conjunction with the [`Hash`] trait. /// /// # Examples /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::Hasher; /// /// let mut hasher = DefaultHasher::new(); /// /// hasher.write_u32(1989); /// hasher.write_u8(11); /// hasher.write_u8(9); /// hasher.write(b"Huh?"); /// /// println!("Hash is {:x}!", hasher.finish()); /// ``` /// /// [`Hash`]: trait.Hash.html /// [`finish`]: #tymethod.finish /// [`write`]: #tymethod.write /// [`write_u8`]: #method.write_u8 #[stable(feature = "rust1", since = "1.0.0")] pub trait Hasher { /// Returns the hash value for the values written so far. /// /// Despite its name, the method does not reset the hasher’s internal /// state. Additional [`write`]s will continue from the current value. /// If you need to start a fresh hash value, you will have to create /// a new hasher. /// /// # Examples /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::Hasher; /// /// let mut hasher = DefaultHasher::new(); /// hasher.write(b"Cool!"); /// /// println!("Hash is {:x}!", hasher.finish()); /// ``` /// /// [`write`]: #tymethod.write #[stable(feature = "rust1", since = "1.0.0")] fn finish(&self) -> u64; /// Writes some data into this `Hasher`. /// /// # Examples /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::Hasher; /// /// let mut hasher = DefaultHasher::new(); /// let data = [0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]; /// /// hasher.write(&data); /// /// println!("Hash is {:x}!", hasher.finish()); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn write(&mut self, bytes: &[u8]); /// Writes a single `u8` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_u8(&mut self, i: u8) { self.write(&[i]) } /// Writes a single `u16` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_u16(&mut self, i: u16) { self.write(&i.to_ne_bytes()) } /// Writes a single `u32` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_u32(&mut self, i: u32) { self.write(&i.to_ne_bytes()) } /// Writes a single `u64` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_u64(&mut self, i: u64) { self.write(&i.to_ne_bytes()) } /// Writes a single `u128` into this hasher. #[inline] #[stable(feature = "i128", since = "1.26.0")] fn write_u128(&mut self, i: u128) { self.write(&i.to_ne_bytes()) } /// Writes a single `usize` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_usize(&mut self, i: usize) { self.write(&i.to_ne_bytes()) } /// Writes a single `i8` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_i8(&mut self, i: i8) { self.write_u8(i as u8) } /// Writes a single `i16` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_i16(&mut self, i: i16) { self.write(&i.to_ne_bytes()) } /// Writes a single `i32` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_i32(&mut self, i: i32) { self.write(&i.to_ne_bytes()) } /// Writes a single `i64` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_i64(&mut self, i: i64) { self.write(&i.to_ne_bytes()) } /// Writes a single `i128` into this hasher. #[inline] #[stable(feature = "i128", since = "1.26.0")] fn write_i128(&mut self, i: i128) { self.write(&i.to_ne_bytes()) } /// Writes a single `isize` into this hasher. #[inline] #[stable(feature = "hasher_write", since = "1.3.0")] fn write_isize(&mut self, i: isize) { self.write(&i.to_ne_bytes()) } } #[stable(feature = "indirect_hasher_impl", since = "1.22.0")] impl<H: Hasher + ?Sized> Hasher for &mut H { fn finish(&self) -> u64 { (**self).finish() } fn write(&mut self, bytes: &[u8]) { (**self).write(bytes) } fn write_u8(&mut self, i: u8) { (**self).write_u8(i) } fn write_u16(&mut self, i: u16) { (**self).write_u16(i) } fn write_u32(&mut self, i: u32) { (**self).write_u32(i) } fn write_u64(&mut self, i: u64) { (**self).write_u64(i) } fn write_u128(&mut self, i: u128) { (**self).write_u128(i) } fn write_usize(&mut self, i: usize) { (**self).write_usize(i) } fn write_i8(&mut self, i: i8) { (**self).write_i8(i) } fn write_i16(&mut self, i: i16) { (**self).write_i16(i) } fn write_i32(&mut self, i: i32) { (**self).write_i32(i) } fn write_i64(&mut self, i: i64) { (**self).write_i64(i) } fn write_i128(&mut self, i: i128) { (**self).write_i128(i) } fn write_isize(&mut self, i: isize) { (**self).write_isize(i) } } /// A trait for creating instances of [`Hasher`]. /// /// A `BuildHasher` is typically used (e.g., by [`HashMap`]) to create /// [`Hasher`]s for each key such that they are hashed independently of one /// another, since [`Hasher`]s contain state. /// /// For each instance of `BuildHasher`, the [`Hasher`]s created by /// [`build_hasher`] should be identical. That is, if the same stream of bytes /// is fed into each hasher, the same output will also be generated. /// /// # Examples /// /// ``` /// use std::collections::hash_map::RandomState; /// use std::hash::{BuildHasher, Hasher}; /// /// let s = RandomState::new(); /// let mut hasher_1 = s.build_hasher(); /// let mut hasher_2 = s.build_hasher(); /// /// hasher_1.write_u32(8128); /// hasher_2.write_u32(8128); /// /// assert_eq!(hasher_1.finish(), hasher_2.finish()); /// ``` /// /// [`build_hasher`]: #tymethod.build_hasher /// [`Hasher`]: trait.Hasher.html /// [`HashMap`]: ../../std/collections/struct.HashMap.html #[stable(since = "1.7.0", feature = "build_hasher")] pub trait BuildHasher { /// Type of the hasher that will be created. #[stable(since = "1.7.0", feature = "build_hasher")] type Hasher: Hasher; /// Creates a new hasher. /// /// Each call to `build_hasher` on the same instance should produce identical /// [`Hasher`]s. /// /// # Examples /// /// ``` /// use std::collections::hash_map::RandomState; /// use std::hash::BuildHasher; /// /// let s = RandomState::new(); /// let new_s = s.build_hasher(); /// ``` /// /// [`Hasher`]: trait.Hasher.html #[stable(since = "1.7.0", feature = "build_hasher")] fn build_hasher(&self) -> Self::Hasher; } /// Used to create a default [`BuildHasher`] instance for types that implement /// [`Hasher`] and [`Default`]. /// /// `BuildHasherDefault<H>` can be used when a type `H` implements [`Hasher`] and /// [`Default`], and you need a corresponding [`BuildHasher`] instance, but none is /// defined. /// /// Any `BuildHasherDefault` is [zero-sized]. It can be created with /// [`default`][method.Default]. When using `BuildHasherDefault` with [`HashMap`] or /// [`HashSet`], this doesn't need to be done, since they implement appropriate /// [`Default`] instances themselves. /// /// # Examples /// /// Using `BuildHasherDefault` to specify a custom [`BuildHasher`] for /// [`HashMap`]: /// /// ``` /// use std::collections::HashMap; /// use std::hash::{BuildHasherDefault, Hasher}; /// /// #[derive(Default)] /// struct MyHasher; /// /// impl Hasher for MyHasher { /// fn write(&mut self, bytes: &[u8]) { /// // Your hashing algorithm goes here! /// unimplemented!() /// } /// /// fn finish(&self) -> u64 { /// // Your hashing algorithm goes here! /// unimplemented!() /// } /// } /// /// type MyBuildHasher = BuildHasherDefault<MyHasher>; /// /// let hash_map = HashMap::<u32, u32, MyBuildHasher>::default(); /// ``` /// /// [`BuildHasher`]: trait.BuildHasher.html /// [`Default`]: ../default/trait.Default.html /// [method.default]: #method.default /// [`Hasher`]: trait.Hasher.html /// [`HashMap`]: ../../std/collections/struct.HashMap.html /// [`HashSet`]: ../../std/collections/struct.HashSet.html /// [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; 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 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 let (a, b) = unsafe { *(self as *const Self as *const (usize, usize)) }; state.write_usize(a); state.write_usize(b); } } } }