6 Language Features

Abstract types:

An abstract type is a compile-time construct which is represented in a different way at runtime. This allows giving a whole new meaning to existing types.

Extern classes:

Externs can be used to describe target-specific interaction in a type-safe manner.

Anonymous structures:

Data can easily be grouped in anonymous structures, minimizing the necessity of small data classes.

var point = {x: 0, y: 10};
point.x += 10;

Array Comprehension:

Create and populate arrays quickly using for loops and logic.

var evenNumbers = [for (i in 0...100) if (i & 1 == 0) i];

Map Comprehension:

Create and populate maps quickly using for loops and logic.

var primality = [for (i in 0...100) i => isPrime(i)];

Classes, interfaces and inheritance:

Haxe allows structuring code in classes, making it an object-oriented language. Common related features known from languages such as Java are supported, including inheritance and interfaces.

Conditional compilation:

Conditional Compilation allows compiling specific code depending on compilation parameters. This is instrumental for abstracting target-specific differences, but can also be used for other purposes, such as more detailed debugging.

#if js
#elseif sys

(Generalized) Algebraic Data Types:

Structure can be expressed through algebraic data types (ADT), which are known as enums in the Haxe Language. Furthermore, Haxe supports their generalized variant known as GADT.

enum Result {
  SystemError(msg:String, position:PosInfos);

Inlined calls:

Functions can be designated as being inline, allowing their code to be inserted at call-site. This can yield significant performance benefits without resorting to code duplication via manual inlining.


Iterating over a set of values, e.g. the elements of an array, is very easy in Haxe courtesy of iterators. Custom classes can quickly implement iterator functionality to allow iteration.

for (i in [1, 2, 3]) {

Local functions and closures:

Functions in Haxe are not limited to class fields and can be declared in expressions as well, allowing powerful closures.

var buffer = "";
function append(s:String) {
  buffer += s;
trace(buffer); // foobar


Add metadata to fields, classes or expressions. This can communicate information to the compiler, macros, or runtime classes.

class MyClass {
  @range(1, 8) var value:Int;
trace(haxe.rtti.Meta.getFields(MyClass).value.range); // [1,8]

Static Extensions:

Existing classes and other types can be augmented with additional functionality through using static extensions.

using StringTools;
"  Me & You    ".trim().htmlEscape();

String Interpolation:

Strings declared with a single quotes are able to access variables in the current context.

trace('My name is $name and I work in ${job.industry}');

Partial function application:

Any function can be applied partially, providing the values of some arguments and leaving the rest to be filled in later.

var map = new haxe.ds.IntMap();
var setToTwelve = map.set.bind(_, 12);

Pattern Matching:

Complex structures can be matched against patterns, extracting information from an enum or a structure and defining specific operations for specific value combination.

var a = {foo: 12};
switch a {
  case {foo: i}: trace(i);


Variable class fields can be designed as properties with custom read and write access, allowing fine grained access control.

public var color(get,set);
function get_color() {
  return element.style.backgroundColor;
function set_color(c:String) {
  trace('Setting background of element to $c');
  return element.style.backgroundColor = c;

Access control:

The access control language feature uses the Haxe metadata syntax to force or allow access classes or fields.

Type Parameters, Constraints and Variance:

Types can be parametrized with type parameters, allowing typed containers and other complex data structures. Type parameters can also be constrained to certain types and respect variance rules.

class Main<A> {
  static function main() {
    new Main<String>("foo");
    new Main(12); // use type inference

  function new(a:A) {}