hashable

A class for types that can be converted to a hash value

http://github.com/haskell-unordered-containers/hashable

LTS Haskell 24.17:1.5.0.0@rev:1
Stackage Nightly 2025-10-31:1.5.0.0@rev:1
Latest on Hackage:1.5.0.0@rev:1

See all snapshots hashable appears in

BSD-3-Clause licensed by Milan Straka <[email protected]> Johan Tibell
Maintained by Oleg Grenrus
This version can be pinned in stack with:hashable-1.5.0.0@sha256:2f23146cbe0325029927b221647695a4c7d6e97548ff731110979e34361f58ef,5914

Module documentation for 1.5.0.0

The hashable package

This package defines a class, Hashable, for types that can be converted to a hash value. This class exists for the benefit of hashing-based data structures. The package provides instances for basic types and a way to combine hash values.

Changes

See also https://pvp.haskell.org/faq

Version 1.5.0.0

  • Add QuantifiedConstraints superclasses to Hashable1/2:
class (Eq1 t, forall a. Hashable a => Hashable (t a)) => Hashable1 t where
class (Eq2 t, forall a. Hashable a => Hashable1 (t a)) => Hashable2 t where

  • Change contexts of Compose, Product and Sum instances. This and above is the similar change as CLC proposal #10

  • The above changes require base-4.18.0.0, so we drop support for GHC prior GHC-9.6.5 (The hashable-1.4 branch will be maintained for time being for older GHC users).

  • Make Arg a b instance behave as Hashable a instance.

Version 1.4.7.0

  • Make arch-native disabled by default.

Version 1.4.6.0

  • Use GND&DerivingVia to derive newtype intances (Data.Semigroup, Data.Monoid, Identity etc).

Version 1.4.5.0

  • Drop support for GHCs prior 8.6.5
  • Use xxhash for hashing bytestrings and bytearrays. Note: when compiling binaries for distribution, you may need to disable arch-native flag.

Version 1.4.4.0

  • Depend on os-string-2 for GHC-9.2+
  • Support filepath-1.5

Version 1.4.3.0

  • Export defaultHashWithSalt and defaultHash.
  • Fix issue of tuples with 0 first component causing all-zero state.
  • Change hashInt to mix bits more.

Version 1.4.2.0

  • Fix the foreign signature of getThreadId https://github.com/haskell-unordered-containers/hashable/pull/263
  • Drop support for GHCs prior GHC-8.2 The recent unordered-containers releases support only GHC-8.2+
  • Add instance for OsString, PosixString, WindowsString from filepath-1.4.100.1
  • Add Hashable ByteArray instance using data-array-byte compat package

Version 1.4.1.0

  • Add instance for Data.Array.Byte.ByteArray.

Version 1.4.0.2

  • Restore older GHC support
  • Support GHC-9.0.2

Version 1.4.0.1

  • text-2.0 compatibility

Version 1.4.0.0

  • Eq is now a superclass of Hashable. Also Eq1 is a superclass of Hashable1 and Eq2 is a superclass of Hashable2 when exists.

  • Remove Hashable1 Fixed instance

  • Remove Hashable1 Semi.Min/Max/... instances as they don’t have Eq1 instance.

Version 1.3.5.0

  • Add Solo instance (base-4.15+, GHC-9+)

Version 1.3.4.1

  • Fix compilation on 32 bit platforms
  • Fix Tree instance

Version 1.3.4.0

Version 1.3.3.0

Version 1.3.2.0

  • Add Hashable (Fixed a) for base <4.7 versions.
  • Add documentation:
    • hashable is not a stable hash
    • hashWithSalt may return negative values
    • there is time-compat with Hashable instances for time types.
  • Add random-initial-seed flag causing the initial seed to be randomized on each start of an executable using hashable.

Version 1.3.1.0

  • Add Hashable1 instances to semigroups types.

  • Use ghc-bignum with GHC-9.0

  • Use FNV-1 constants.

  • Make hashable-examples a test-suite

Version 1.3.0.0

  • Semantic change of Hashable Arg instance to not hash the second argument of Arg in order to be consistent with Eq Arg (#171)

  • Semantic change of Hashable Float and Hashable Double instances to hash -0.0 and 0.0 to the same value (#173)

  • Add Hashable instance for Fingerprint (#156)

  • Add new Data.Hashable.Generic module providing the default implementations genericHashWithSalt and genericLiftHashWithSalt together with other Generics support helpers (#148, #178)

  • Bump minimum version requirement of base to base-4.5 (i.e. GHC >= 7.4)

Version 1.2.7.0

  • Add Hashable and Hashable1 instances for Complex

  • Fix undefined behavior in hashable_fn_hash() implementation due to signed integer overflow (#152)

  • Mark Data.Hashable.Lifted as Trustworthy (re SafeHaskell)

  • Support GHC 8.4

Version 1.2.6.1

  • Use typeRepFingerprint from Type.Reflection.Unsafe

  • Bump minimum version of base to 4.4.

Version 1.2.6.0

  • Add support for type-indexed Typeable.

  • Rework the Generic hashable for sums.

Version 1.2.5.0

  • Add Hashable1 and Hashable2

  • Add instances for: Eq1, Ord1, Show1, Ptr, FunPtr, IntPtr, WordPtr

  • Add Hashed type for caching the hash function result.

Version 1.2.4.0

  • Add instances for: Unique, Version, Fixed, NonEmpty, Min, Max, Arg, First, Last, WrappedMonoid, Option

  • Support GHC 8.0

Version 1.2.3.3

  • Support integer-simple.

Version 1.2.3.2

  • Add support for GHC 7.10 typeRepFingerprint

Version 1.2.3.1

  • Added support for random 1.1.*.

Version 1.2.3.0

  • Silence integer literal overflow warning

  • Add support for GHC 7.10 integer-gmp2 & Natural

  • Add instance for Data.Void

  • Make the SSE .cabal flags manual

  • Add an upper bound on bytestring

Version 1.2.2.0

  • Add instances for Data.ByteString.Short

  • Use a 32-bit default salt on 32-bit archs.

Version 1.2.1.0

  • Revert instances to their 1.1 implementations to regain the performance we had then.

  • Remove use of random salt altogether. Without using SipHash the benefit is unclear (i.e. collision attacks still work) and the complexity is no longer worth it.

  • Documentation improvements.

Version 1.2.0.10

  • Fix for GHC 7.0.

Version 1.2.0.9

  • Stop using SipHash. The current implementation still has segfault causing bugs that we won’t be able to fix soon.

  • Stop using Wang hash. It degrades performance of fixed-size integer hashing too much.

Version 1.2.0.8

  • Fix linking issue when SSE was disabled.

  • Hash small signed Integers correctly.

Version 1.2.0.7

  • Add flags to control usage of SSE.

Version 1.2.0.6

  • Fix another segfault caused by SSE2 code.

Version 1.2.0.5

  • More portability fixes.

  • Force stack alignment to 16 bytes everywhere. Fixes a segfault.

  • Fix bug where code relied on rewrite rules firing for correctness.

Version 1.2.0.4

  • Update docs to match code.

  • Work around bug in GHCi runtime linker, which never call static initializers.

Version 1.2.0.3

  • Make building of SSE 4.1 code conditional, as it doesn’t work on all platforms.

  • Use a fixed salt, but allow random salting. Random salting by default broke people’s code.

Version 1.2.0.2

  • Work around ghci linker bug on Windows.

Version 1.2.0.1

  • Fix performance bug in SSE implementation of SipHash.

  • Fix segfault due to incorrect stack alignment on Windows.

Version 1.2.0.0

  • Switch string hashing from FNV-1 to SipHash, in an effort to prevent collision attacks.

  • Switch fixed-size integer hashing to Wang hash.

  • The default salt now switched on every program run, in an effort to prevent collision attacks.

  • Move hash method out of Hashable type class.

  • Add support for generic instance deriving.

  • Add instance for Ordering.

Version 1.1.2.5

  • Bug fix for bytestring < 0.10.0.

Version 1.1.2.4

  • Switch string hashing from Bernstein to FNV-1

  • Faster instance for Integer.

  • Update dependency on base, ghc-prim

  • Now works with GHC 7.6.

Version 1.1.2.3

  • Add instance for TypeRep.

  • Update dependency on test-framework.

Version 1.1.2.2

  • Bug fix for GHC 7.4

Version 1.1.2.1

  • Update dependency on test-framework.

  • Improve documentation of combine.

Version 1.1.2.0

  • Fix hash collision issues for lists and tuples when using a user-specified salt.

  • Add instances for Integer, Ratio, Float, Double, and StableName.

  • Improved instances for tuples and lists.

Version 1.1.1.0

  • Add hashWithSalt, which allows the user to create different hash values for the same input by providing different seeds. This is useful for application like Cuckoo hashing which need a family of hash functions.

  • Fix a bug in the Hashable instance for Int64/Word64 on 32-bit platforms.

  • Improved resilience to leading zero in the input being hashed.

Version 1.1.0.0

  • Add instance for: strict and lazy Texts, ThreadId

  • Add hashPtrWithSalt and hashByteArrayWithSalt.

  • Faster ByteArray# hashing.

  • Fix a signedness bug that affected ByteString.

  • Fix ByteString hashing to work correctly on both 32 and 64-bit platforms.

Version 1.0.1.1

  • Fix bug in Hashable instance for lazy ByteStrings where differences in the internal structure of the ByteString could cause different hash values for ByteStrings that are equal according to ==.

Version 1.0.1.0

  • Add two helpers for creating Hashable instances: hashPtr and hashByteArray.

Version 1.0.0

  • Separate Hashable class to its own package from hashmap 1.0.0.3.