Go🔧Core Languagebeginner

Maps

Go · Core Language · Run with go run

Explanation

A `map[K]V` is Go's built-in hash map. Keys must be `comparable` (no slices, maps, or functions as keys). The zero value of a map is `nil` — attempting to write to a nil map panics. Always initialize with `make` or a literal. The two-value assignment `v, ok := m[key]` safely checks for key presence without panicking on missing keys.

Real-World Scenario

Counting word frequencies in a document: `counts := make(map[string]int)` then `counts[word]++` — the zero value of `int` (0) means missing keys auto-initialize correctly.

Quick Snippet

snippet.go

// Literal initialization
scores := map[string]int{
    "Alice": 95,
    "Bob":   87,
}

// Safe lookup
score, ok := scores["Charlie"]
if !ok {
    fmt.Println("not found")
}

// Delete
delete(scores, "Bob")

// Iterate (order is random)
for name, s := range scores {
    fmt.Println(name, s)
}

Full Example

View on GitHub

maps.go

// Compile: go run maps.go
// Output:
//   Alice: 95
//   Charlie present: false
//   after delete, has Bob: false
//   total entries: 1
package main

import "fmt"

func main() {
	scores := map[string]int{
		"Alice": 95,
		"Bob":   87,
	}

	fmt.Println("Alice:", scores["Alice"])

	// Comma-ok lookup — safe check for missing keys
	_, ok := scores["Charlie"]
	fmt.Println("Charlie present:", ok)

	delete(scores, "Bob")
	_, hasBob := scores["Bob"]
	fmt.Println("after delete, has Bob:", hasBob)

	fmt.Println("total entries:", len(scores))
}

Run command

bash

go run maps.go

Arrays and Slices

Error Handling