The maps Package

The generic maps package helps clone, compare and iterate Go map collections.

maps.Clone creates a shallow copy of the map entries; maps.Equal compares map key/value pairs when values are comparable. Map iteration order is unspecified, so sort keys before generating predictable output or displaying sorted results.

Go 1.23 added maps.Keys and related iterator helpers. A clone of a map containing slices or pointers shares referenced nested data unless you copy those values separately.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"fmt"
	"maps"
)

func main() {
	original := map[string]int{"apples": 2, "pears": 3}
	copied := maps.Clone(original)
	copied["apples"] = 5
	fmt.Println("Original apples:", original["apples"])
	fmt.Println("Copy apples:", copied["apples"])
	fmt.Println("Equal:", maps.Equal(original, copied))
}

Output

Original apples: 2
Copy apples: 5
Equal: false

The copied map has independent entries, so updating copied["apples"] leaves original["apples"] equal to 2. The two maps no longer compare equal.

• Cloning does not recursively clone pointer or slice values stored in map entries.
• Do not rely on the order of range over a map.

Add a new key to the cloned map and use maps.Equal to compare before and after the change.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced The maps Package in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.