maps.go

// _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 `""`. Here we didn't need the value
	// itself, so we ignored it with the _blank identifier_
	// `_`.
	_, 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)
}