HaxeDoc2

Chapter 2

2 Types

The Haxe Compiler employs a rich type system which helps detecting type-related errors in a

program at compile-time. A type error is an invalid operation on a given type such as dividing

by a String, trying to access a field of an Integer or calling a function with not enough (or too

many) arguments.

In some languages this additional safety comes at a price because programmers are forced to

explicitly assign types to syntactic constructs:

1 var myButton:MySpecialButton =
2 new MySpecialButton(); // As
3 MySpecialButton* myButton =
4 new MySpecialButton(); // C++

The explicit type annotations are not required in Haxe, because the compiler caninferthe type:

1 var myButton = new MySpecialButton(); // Haxe

We will explore type inference in detail later inType Inference(Section 3.6). For now, it is suf-

ficient to say that the variablemyButtonin the above code is known to be aninstance of class

MySpecialButton.

The Haxe type system knows seven type groups:

Class instance: an object of a given class or interface

Enum instance: a value of a Haxe enumeration

Structure:an anonymous structure, i.e. a collection of named fields

Function:a compound type of several arguments and one return

Dynamic:a wildcard type which is compatible with any type

Abstract:a compile-time type which is represented by a different type at runtime

Monomorph: an unknown type which may later become a different type

We will describe each of these type groups and how they relate to each other in the next

chapters.

Definition: Compound Type

A compound type is a type which has sub-types. This includes any type with type parameters

(3.2) and the function (2.6) type.