Maps

Create and set values

Use make or a literal. Keys must be comparable types.

ages := map[string]int{
	"Ada": 28,
	"Lin": 22,
}
ages["Sam"] = 30
fmt.Println(ages["Ada"])

Check if a key exists

The two-value form tells you whether the key was present.

age, ok := ages["Kai"]
if !ok {
	fmt.Println("not found")
} else {
	fmt.Println(age)
}

Delete a key

delete removes a key if it exists.

delete(ages, "Lin")
fmt.Println(ages)

Map tips

• Ranging over a map has no fixed order
• Never write to a nil map—initialize first
• Maps are reference-like: assignments share the same map
• Choose key types carefully; structs work if all fields are comparable