Haxe 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.

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%2==0) 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
	js.Lib.alert("Hello");
#elseif sys
	Sys.println("Hello");
#end

(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 {
	Success(data:Array<Int>);
	UserError(msg:String);
	SystemError(msg:String, position:PosInfos);
}

Inlined calls: Functions can be designed 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.

Iterators: 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]) {
	trace(i);
}

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;
}
append("foo");
append("bar");
trace(buffer); // foobar

Metadata: 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);
setToTwelve(1);
setToTwelve(2);

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);
	default:
}

Properties: 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;
}

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) { }
}