less pointers and more memory-efficient Clear()

`threadUnsafeSet` is already a map that is a reference-type, so passing it by-value still lets us mutate an origin object, but decreases a number of pointers, which in turn, decreases a GC-pressure, (potentially) makes less useless operations and (definitely) makes code better to read/understand.

Another point of the change is to a bit "upgrade" a `Clear()` method. In the old implementation, it simply constructed a new `threadUnsafeSet` and did mutate an origin pointer to point at our new set. This commits an extra allocation (I would expect a `Clear()` method to be allocations-free), and fallbacks already allocated map's size to the default one. So I replaced this with clearing itself using `mapclear()` function (that implicitly replaces `for key := range d { delete(d, key) }`). This is actually pretty expensive operation, but does no allocations, that is maybe even cheaper than vice-versa. Anyway user always can construct a new instance of the set by itself, but cannot clear underlying map manually in case he really needs it - to decrease amount of memory used in average, number of which is actually affected a lot by internally allocating a new map
1 file changed
tree: 3a8f8c4dbbec1613c564928acbd0f76a4b39bc75
  1. .github/
  2. .gitignore
  3. bench_test.go
  4. go.mod
  5. go.sum
  6. iterator.go
  7. iterator_example_test.go
  9. new_improved.jpeg
  10. README.md
  11. set.go
  12. set_test.go
  13. threadsafe.go
  14. threadsafe_test.go
  15. threadunsafe.go

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The missing generic set collection for the Go language. Until Go has sets built-in...use this.

Update 3/26/2022

  • Packaged version: 2.0.0 release for generics support with breaking changes.
  • supports new generic syntax
  • Go 1.18.0 or higher

With Generics

Coming from Python one of the things I miss is the superbly wonderful set collection. This is my attempt to mimic the primary features of the set collection from Python. You can of course argue that there is no need for a set in Go, otherwise the creators would have added one to the standard library. To those I say simply ignore this repository and carry-on and to the rest that find this useful please contribute in helping me make it better by contributing with suggestions or PRs.


  • NEW Generics based implementation (requires Go 1.18 or higher)
  • One common interface to both implementations
    • a non threadsafe implementation favoring performance
    • a threadsafe implementation favoring concurrent use
  • Feature complete set implementation modeled after Python's set implementation.
  • Exhaustive unit-test and benchmark suite

Trusted by

This package is trusted by many companies and thousands of open-source packages. Here are just a few sample users of this package.

  • Notable projects/companies using this package
    • Ethereum
    • Docker
    • 1Password
    • Hashicorp

Star History

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The code below demonstrates how a Set collection can better manage data and actually minimize boilerplate and needless loops in code. This package now fully supports generic syntax so you are now able to instantiate a collection for any comparable type object.

What is considered comparable in Go?

  • Booleans, integers, strings, floats or basically primitive types.
  • Pointers
  • Arrays
  • Structs if all of their fields are also comparable independently

Using this library is as simple as creating either a threadsafe or non-threadsafe set and providing a comparable type for instantiation of the collection.

// Syntax example, doesn't compile.
mySet := mapset.NewSet[T]() // where T is some concrete comparable type.

// Therefore this code creates an int set
mySet := mapset.NewSet[int]()

// Or perhaps you want a string set
mySet := mapset.NewSet[string]()

type myStruct {
  name string
  age uint8

// Alternatively a set of structs
mySet := mapset.NewSet[myStruct]()

// Lastly a set that can hold anything using the any or empty interface keyword: interface{}. This is effectively removes type safety.
mySet := mapset.NewSet[any]()

Comprehensive Example

package main

import (
  mapset "github.com/deckarep/golang-set/v2"

func main() {
  // Create a string-based set of required classes.
  required := mapset.NewSet[string]()

  // Create a string-based set of science classes.
  sciences := mapset.NewSet[string]()
  // Create a string-based set of electives.
  electives := mapset.NewSet[string]()

  // Create a string-based set of bonus programming classes.
  bonus := mapset.NewSet[string]()
  bonus.Add("beginner go")
  bonus.Add("python for dummies")

Create a set of all unique classes. Sets will automatically deduplicate the same data.

  all := required


Set{cooking, english, math, chemistry, welding, biology, music, automotive, beginner go, python for dummies}

Is cooking considered a science class?

result := sciences.Contains("cooking")



Show me all classes that are not science classes, since I don't enjoy science.

notScience := all.Difference(sciences)
Set{ music, automotive, beginner go, python for dummies, cooking, english, math, welding }

Which science classes are also required classes?

reqScience := sciences.Intersect(required)



How many bonus classes do you offer?




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