The new Map syntax in Haxe 3

I was using the Haxe3 Release Candidate for well over a month before I realised that the new Map data structures could be created with a nice syntax.  The basic gist is this:

var map1 = [ 1=>"one", 2=>"two", 3=>"three" ];

Like Arrays, but you use the “=>” operator to define both the key and the value.  And Haxe’s type inference is as strong as ever.  Here’s what the compiler picks up:

var map1 = [ 1=>"one", 2=>"two", 3=>"three" ];
$type (map1); // Map<Int, String>

var map2 = [ "one"=>1, "two"=>2, "three"=>3 ];
$type (map2); // Map<String, Int>

var map3 = [
    Date.now() => "Today",
    Date.now().delta(24*60*60*1000) => "Tomorrow",
    Date.now().delta(-24*60*60*1000) => "Yesterday"
];
$type (map3); // Map<Date, String>

var map4 = [
    { name: "Tony Stark" } => "Iron Man",
    { name: "Peter Parker" } => "Spider Man"
];
$type (map4); // Map<{ name : String }, String>

var map5 = [
    [1,2] => ["one","two"],
    [3,4] => ["three","four"],
];
$type (map5); // Map<Array<Int>, Array<String>>

So it’s pretty clever.  If for some reason you need to type explicitly to StringMap, IntMap, or ObjectMap, you can:

var stringMap:StringMap<Int> = [
    "One" => 1,
    "Two" => 2
];
$type(stringMap); // haxe.ds.StringMap<Int>

var intMap:IntMap<String> = [
    1 => "One",
    2 => "Two"
];
$type(intMap); // haxe.ds.IntMap<String>

var objectMap:ObjectMap<{ name:String }, String> = [
    { name: "Tony Stark" } => "Iron Man",
    { name: "Peter Parker" } => "Spider Man"
];
$type(objectMap); // haxe.ds.ObjectMap<{ name : String }, String>

But if you try to do anything too funky with types, the compiler will complain.  Haxe likes to keep things strictly typed:

var funkyMap = [
    { name: "Tony Stark" } => "Iron Man",
    { value: "Age" } => 25
]; // Error: { value : String } has no field name ... 
   // you are a bad person, and your items are not comprehensible 
   // to Haxe's typing system

Finally, Haxe won’t let you do define duplicate keys using this syntax:

var mapWithDuplicates = [
    1 => "One",
    2 => "Two",
    1 => "uno"
]; // Error: Duplicate Key ... previously defined (somewhere)

If you’re using an object map, it’s only a duplicate if you’re dealing with the exact same object, not a similar one.  For example, this is allowed:

var similarObjectKeys:ObjectMap<Array<Int>, String> = [
    [0] => "First Array object",
    [0] => "Second Array object"
]; // Works, you now have 2 items in your map.

But if you use the exact same object, Haxe will pick it up:

var key = [0];
var sameObjectKey = [
    key => "First Array object",
    key => "Second Array object"
]; // Error: Duplicate Key ...

So there you have it.  A nice feature that I didn’t see mentioned anywhere else.  Thanks Haxe team!

….

Update:

It’s worth mentioning that once you have created your map, you can use array access (“[” and “]”) to read or modify entries in your map.

var map = [ 1=>"one", 2=>"two", 3=>"three" ];

// Reading a value
map[1];   "one"
var i = 2;
map[i];   "two"
map[++i]; "three"

// Setting a value
map[4] = "four";
map[1] = "uno";
map[i] = "THREE";
map;   // [ 1=>"uno", 2=>"two", 3=>"THREE", 4=>"four" ]