map

// _Maps_ are Go's built-in [associative data type](http://en.wikipedia.org/wiki/Associative_array)

// (sometimes called _hashes_ or _dicts_ in other languages).

package main

import "fmt"

func main() {

// To create an empty map, use the builtin `make`:

// `make(map[key-type]val-type)`.

m := make(map[string]int)

// Set key/value pairs using typical `name[key] = val`

// syntax.

m["k1"] = 7

m["k2"] = 13

// Printing a map with e.g. `Println` will show all of

// its key/value pairs.

fmt.Println("map:", m)

// Get a value for a key with `name[key]`.

v1 := m["k1"]

fmt.Println("v1: ", v1)

// The builtin `len` returns the number of key/value

// pairs when called on a map.

fmt.Println("len:", len(m))

// The builtin `delete` removes key/value pairs from

// a map.

delete(m, "k2")

fmt.Println("map:", m)

// The optional second return value when getting a

// value from a map indicates if the key was present

// in the map. This can be used to disambiguate

// between missing keys and keys with zero values

// like `0` or `""`.

_, prs := m["k2"]

fmt.Println("prs:", prs)

// You can also declare and initialize a new map in

// the same line with this syntax.

n := map[string]int{"foo": 1, "bar": 2}

fmt.Println("map:", n)

}