Maps

A map stores key-value pairs, declared with map[KeyType]ValueType. Map literals and assignment both use familiar syntax, and looking up a missing key doesn't panic — it just returns the value type's zero value.

package main

import "fmt"

func main() {
	scores := map[string]int{"Alice": 95, "Bob": 87}
	scores["Carol"] = 91

	fmt.Println(scores["Alice"])
	fmt.Println(scores["Carol"])
}

95
91

The comma-ok idiom

Because a missing key silently returns a zero value, Go gives you a second return value to tell the two cases apart: value, ok := m[key] sets ok to false if the key wasn't present, letting you distinguish "key genuinely maps to zero" from "key doesn't exist at all".

package main

import "fmt"

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

	value, ok := scores["Dave"]
	fmt.Println(value, ok)

	value, ok = scores["Alice"]
	fmt.Println(value, ok)
}

0 false
95 true

Next: structs — grouping related data together.