How to Use the cmp Package for Comparison Functions

Stdlib
2026-04-17T12:05:42+00:00
Use `cmp.Compare` to compare two values of the same type, returning -1, 0, or 1 to indicate less than, equal, or greater than. This function replaces manual comparison logic for any comparable type.

How to Use the cmp Package for Comparison Functions

Use cmp.Compare to compare two values of the same type, returning -1, 0, or 1 to indicate less than, equal, or greater than. This function replaces manual comparison logic for any comparable type.

package main

import (
	"fmt"
	"cmp"
)

func main() {
	a := []int{1, 2, 3}
	b := []int{1, 2, 4}

	result := cmp.Compare(a, b)
	fmt.Println(result) // result is -1 because a < b
}

For sorting slices, use cmp.Ordered with slices.SortFunc or slices.BinarySearchFunc.

package main

import (
	"fmt"
	"cmp"
	"slices"
)

func main() {
	items := []string{"b", "a", "c"}
	slices.SortFunc(items, cmp.Compare[string])
	fmt.Println(items) // items is now ["a", "b", "c"]
}

For custom comparison logic, pass a function to slices.SortFunc.

package main

import (
	"fmt"
	"cmp"
	"slices"
)

func main() {
	items := []string{"apple", "pear", "kiwi", "banana"}
	slices.SortFunc(items, func(a, b string) int {
		return cmp.Compare(len(a), len(b))
	})
	fmt.Println(items) // Sorted by length: ["pear", "kiwi", "apple", "banana"]
}

The cmp package also provides Less, Greater, Equal, and Max/Min functions for specific use cases.

package main

import (
	"fmt"
	"cmp"
)

func main() {
	a := 10
	b := 20

	if cmp.Less(a, b) {
		fmt.Println("a is less than b")
	}

	maxVal := cmp.Max(a, b)
	fmt.Println(maxVal) // Output: 20
}

For comparing values of different types, use type assertions or explicit conversions before calling cmp.Compare.