GenericStack Option

10.2.5 Map

A Map is a container composed of key, value pairs. A Map is also commonly referred to as an associative array, dictionary, or symbol table. The following code gives a short example of working with maps:

class Main {
  static public function main() {
    // Maps are initialized like arrays, but
    // use the map literal syntax with the
    // '=>' operator. Maps can have their
    // key value types defined explicity
    var map1:Map<Int, String> = [1 => "one", 2 => "two"];

    // Or they can infer their key value types
    var map2 = ["one" => 1, "two" => 2, "three" => 3];
    $type(map2); // Map<String, Int>

    // Keys must be unique
    // Error: Duplicate Key
    // var map3 = [1=>"dog", 1=>"cat"];

    // Maps values can be accessed using array
    // accessors "[]"
    var map4 = ["M" => "Monday", "T" => "Tuesday"];
    trace(map4["M"]); // Monday

    // Maps iterate over their values by
    // default
    for (value in map4) {
      trace(value); // Monday \n Tuesday
    }

    // Can iterate over keys by using the
    // keys() method
    for (key in map4.keys()) {
      trace(key); // traces M, then T
    }

    // Like arrays, a new Map can be made using
    // comprehension
    var map5 = [
      for (key in map4.keys())
        key => "FRIDAY!!"
    ];
    // {M => FRIDAY!!, T => FRIDAY!!}
    trace(map5);
  }
}

Under the hood, a Map is an abstract type. At compile time, it gets converted to one of several specialized types depending on the key type:

String: haxe.ds.StringMap
Int: haxe.ds.IntMap
EnumValue: haxe.ds.EnumValueMap
{}: haxe.ds.ObjectMap

The Map type does not exist at runtime and has been replaced with one of the above objects.

Map defines array access using its key type.