Maps

A map stores key-value pairs and lets you look up a value quickly by its key. Keys are unique within a map.

Creating a map

Use make or a literal.

ages := make(map[string]int)
ages["Ada"] = 36
ages["Alan"] = 41
fmt.Println(ages) // map[Ada:36 Alan:41]

Literal form:

scores := map[string]int{
    "math":    90,
    "science": 85,
}

Accessing values

Reading a missing key returns the value type’s zero value.

fmt.Println(scores["math"])    // 90
fmt.Println(scores["history"]) // 0 (not present)

The comma-ok idiom

To tell a real zero from a missing key, use the second return value.

value, ok := scores["history"]
if ok {
    fmt.Println("Found:", value)
} else {
    fmt.Println("Not present")
}

delete

Remove a key with the built-in delete.

delete(scores, "science")
fmt.Println(scores) // map[math:90]