Go Maps

How it works

A map stores key-value pairs. The comma-ok form distinguishes a missing key from a stored zero value. make or a map literal creates a writable map; a nil map permits reads but panics on assignment. delete removes a key and is harmless when the key is absent.

Run this Go example

Install Go separately from the official Go downloads and check go version in a new terminal. The reviewed baseline is Go 1.27.3 on Windows amd64; the authored syntax and standard-library APIs require Go 1.22 or newer. Save the complete source below as maps.go in a learning folder, then run go run maps.go from that folder. These examples use only the standard library.

Bhylu has no Go browser runner. Apache, MySQL, PHP and the JavaScript or Python playground are not required to run these files. File examples own a temporary directory; HTTP client examples create an ephemeral loopback server and close it. They do not contact an external API.

Download the complete maps.go · Download all source files with hash checks

For the optional collection download, save download-examples.mjs in a new learning folder and run node download-examples.mjs. A local preview uses node download-examples.mjs http://127.0.0.1:8000/examples/go/. The downloader refuses an existing bhylu-go-examples folder and installs or executes no Go code.

Example

package main

import (
	"fmt"
)

func main() {
	counts := map[string]int{"A": 0, "B": 4}
	value, exists := counts["A"]
	_, missingExists := counts["C"]
	counts["C"] = 2
	delete(counts, "B")
	fmt.Println(value, exists, missingExists, len(counts))
}

Expected result

0 true false 2

The stored zero in A is a real entry. The missing C initially returns zero with false, then the assignment inserts it. Only comparable types can be keys; a slice is not comparable.