unordered-containers

0.2.21 - December 2025

• API enhancements:

  • Add HashMap.lookupKey and HashSet.lookupElement
  • Add differenceWithKey
  • Add disjoint

• Performance improvements:

  • HashSet.fromList: Use unsafeInsert
  • Use tree-diffing for difference
  • Remove some unnecessary forcing of HashMaps
  • Remove the Array.index function
  • hashWithSalt: Ensure that the salt Int is unboxed

• Documentation changes:

  • Turn some comments into docstrings
  • Reword disclaimer regarding hash collision attacks
  • Update time complexity of some HashSet functions
  • Update instructions for code inspection

• Other changes:

  • Drop support for GHC < 8.10
  • Address deprecation warnings and other warnings
  • Optimize indexing in arrays of length 2
  • Introduce ShiftedHash
  • New “fine-grained” benchmarks
  • Make it compile with MicroHs. Thanks, @augustss!
  • Remove redundant Eq constraints
  • Refactor delete
  • difference[With]: Undo constraint relaxation

0.2.20.1 - October 2025

• Fix infinite loop in isSubmapOf[By] / isSubsetOf on 32-bit platforms. To fix this bug and potentially other similar bugs, we return to a branching factor of 16 on 32-bit platforms.

• Relax bounds for GHC 9.12

• Require hashable >= 1.4

• Documentation changes:

  • Fix documentation about branching factor in Data.HashMap.Strict
  • Improve documentation for Data.HashMap.compose
  • Fixes docs of Data.HashMap.Lazy.fromList: it takes O(n * log(n))
  • Add disclaimer to Data.HashSet.toList

• Remove bad isSubmapOf testcase

0.2.20 - January 2024

• Allow template-haskell-2.21

• Rename confusing variables

• Deal with introduction of Prelude.foldl'

• Remove redundant Hashable constraints from intersection.* and union.*.

• Various optimizations and cleanups: #458, #469, #404, #460, #456, #433

• Add invariant tests: #444, #455

• Improve test case generation

• Improve test failure reporting

0.2.19.1 – April 2022

• Fix bug in intersection[With[Key]]

• Improve docs of bit twiddling functions

0.2.19.0 – April 2022

• Make intersections much faster

• Fix undefined behaviour on 32-bit platforms

• Speed up some array-appending operations: #407, #409

• Use MathJax format for complexity annotations

0.2.18.0

• Fix strictness properties of Strict.mapMaybe[WithKey]

• Fix strictness properties of Strict.alterFEager

• Fix space leaks in union[With[Key]]

• Fix space leak in Lazy.fromListWith

• Speed up difference* and intersection* with unsafeInsert

• unionArrayBy: Find next 1-bits with countTrailingZeros

  • This speeds up union* for sparsely filled nodes, while penalizing union operations on densely filled nodes.

• Reduce reboxing in internal array operations

• Reduce code size of array operations in union*

0.2.17.0

• Define dataCast1 for HashMap

• Add Lift instances for Template Haskell

• Add definitions for stimes

• Expose internal constructors for HashSet, Array and MArray

• Tweak internal Array.insertM function

• Drop support for GHC 8.0

• Drop support for hashable < 1.2.5

• Various cleanup and documentation improvements

0.2.16.0

• Increase maximum branching factor from 16 to 32

• Tweak union.goDifferentHash

• Fix debug mode bounds check in cloneM

• Remove some old internal compatibility code

0.2.15.0

• Add security advisory regarding hash collision attacks

• Add support for hashable 1.4

• Drop support for GHC < 8

0.2.14.0

• Add HashMap.mapKeys. Thanks, Marco Perone!

• Add instances for NFData1 and NFData2. Thanks, Isaac Elliott and Oleg Grenrus!

• Fix @since-annotation for compose. Thanks, @Mathnerd314!

0.2.13.0

• Add HashMap.compose. Thanks Alexandre Esteves.

0.2.12.0

• Add HashMap.isSubmapOf[By] and HashSet.isSubsetOf. Thanks Sven Keidel. (#282)

• Expose internal modules. (#283)

• Documentation improvements in Data.HashSet, including a beginner-friendly introduction. Thanks Matt Renaud. (#267)

• HashMap.alterF: Skip key deletion for absent keys. (#288)

• Remove custom unsafeShift{L,R} definitions. (#281)

• Various other documentation improvements.

0.2.11.0

• Add HashMap.findWithDefault (soft-deprecates HashMap.lookupDefault). Thanks, Matt Renaud.

• Add HashMap.fromListWithKey. Thanks, Josef Svenningsson.

• Add more folding functions and use them in Foldable instances. Thanks, David Feuer.

• Add HashMap.!?, a flipped version of lookup. Thanks, Matt Renaud.

• Add a Bifoldable instance for HashMap. Thanks, Joseph Sible.

• Add a HasCallStack constraint to (!). Thanks, Roman Cheplyaka.

Bug fixes

• Fix a space leak affecting updates on keys with hash collisions. Thanks, Neil Mitchell. (#254)

• Get rid of some silly thunks that could be left lying around. (#232). Thanks, David Feuer.

Other changes

• Speed up the Hashable instances for HashMap and HashSet. Thanks, Edward Amsden.

• Remove a dependency cycle hack from the benchmark suite. Thanks, Andrew Martin.

• Improve documentation. Thanks, Tristan McLeay, Li-yao Xia, Gareth Smith, Simon Jakobi, Sergey Vinokurov, and likely others.

0.2.10.0

• Add HashMap.alterF.

• Add HashMap.keysSet.

• Make HashMap.Strict.traverseWithKey force the results before installing them in the map.

0.2.9.0

• Add Ord/Ord1/Ord2 instances. (Thanks, Oleg Grenrus)

• Use SmallArray# instead of Array# for GHC versions 7.10 and above. (Thanks, Dmitry Ivanov)

• Adjust for Semigroup => Monoid proposal implementation. (Thanks, Ryan Scott)

Bug fixes

• Fix a strictness bug in fromListWith.

• Enable eager blackholing for pre-8.2 GHC versions to work around a runtime system bug. (Thanks, Ben Gamari)

• Avoid sketchy reimplementation of ST when compiling with recent GHC.

Other changes

• Remove support for GHC versions before 7.8. (Thanks, Dmitry Ivanov)

• Add internal documentaton. (Thanks, Johan Tibell)

0.2.8.0

• Add Eq1/2, Show1/2, Read1 instances with base-4.9

• Eq (HashSet a) doesn’t require Hashable a anymore, only Eq a.

• Add Hashable1/2 with hashable-1.2.6.0

• Add differenceWith function.

0.2.7.2

• Don’t use -fregs-graphs

• Fix benchmark compilation on stack.

0.2.7.1

• Fix linker error related to popcnt.

• Haddock improvements.

• Fix benchmark compilation when downloaded from Hackage.

0.2.7.0

• Support criterion 1.1

• Add unionWithKey for hash maps.

0.2.6.0

• Mark several modules as Trustworthy.

• Add Hashable instances for HashMap and HashSet.

• Add mapMaybe, mapMaybeWithKey, update, alter, and intersectionWithKey.

• Add roles.

• Add Hashable and Semigroup instances.

0.2.5.1 (2014-10-11)

• Support base-4.8