set

set is a small, fast, generic Set for Go: an unordered collection of unique elements of a comparable type, built directly on the built-in map.

An element's identity is the language's own equality (==). Two elements are the same if and only if they compare equal, and the runtime map decides uniqueness — there is no hashing, no reflection and no custom equality contract. As a result a Set can never silently drop an element to a collision, and Len always reflects the true number of distinct elements.

• Generic over any comparable element type; exact == identity.
• Full set algebra (Union, Intersection, Difference, SymmetricDifference) and relations (Equal, IsSubset, IsSuperset, IsProperSubset, IsProperSuperset, IsDisjoint).
• Functional helpers: Map, Filter, Reduce, Fold, Any, All.
• iter.Seq[T] iteration for range, plus AddSeq / Collect.
• Usable zero value: var s set.Set[int] is an empty, ready-to-use set.
• JSON serialization through the standard encoding/json interfaces.
• Zero dependencies.

go get github.com/goloop/set/v2

import "github.com/goloop/set/v2"

Requires Go 1.24 or newer. The package has no third-party dependencies.

package main

import (
    "fmt"

    "github.com/goloop/set/v2"
)

func main() {
    ints := set.New[int]()          // empty; element type explicit
    words := set.New("one", "two")  // or inferred from the elements

    ints.Add(1, 2, 3, 4)
    words.Add("two", "three")       // "two" is already present

    fmt.Println(ints.Len())         // 4
    fmt.Println(set.Sorted(ints))   // [1 2 3 4]
    fmt.Println(ints.Contains(3))   // true

    // Set algebra (each accepts several sets at once).
    a := set.New(1, 3, 5, 7)
    b := set.New(0, 2, 4, 7)
    fmt.Println(set.Sorted(a.Intersection(b))) // [7]
    fmt.Println(a.IsDisjoint(set.New(8, 9)))   // true
}

A Set is not safe for concurrent use, like the built-in map it is built on — synchronize externally if a shared set is mutated from several goroutines.

• Full reference and recipes: DOC.md · DOC.UK.md
• Package API: pkg.go.dev/github.com/goloop/set/v2
• Changes between versions: CHANGELOG.md

Contributions are welcome. Please run go test ./..., go vet ./... and gofmt -l . before submitting a pull request.

set is released under the MIT License. See LICENSE.