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It is common for programming languages to have a single, clean definition for nullability. How-

ever, Haxe has to find a compromise in this regard due to the nature of Haxe’s target languages:

While some of them allow and; in fact, default tonullfor anything, others do not even allow

nullfor certain types. This necessitates the distinction of two types of target languages:

Definition: Static target

Static targets employ their own type system wherenullis not a valid value for basic types.

This is true for the Flash, C++, Java and C# targets.

Definition: Dynamic target

Dynamic targets are more lenient with their types and allownullvalues for basic types.

This applies to the JavaScript, PHP, Neko and Flash 6-8 targets.

There is nothing to worry about when working withnullon dynamic targets; however, static
for starters...please re- ones may require some thought. For starters, basic types are initialized to their default values.
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for starters...please re-
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Definition: Default values

Basic types have the following default values on static targets:

Int: 0

Float: NaNon Flash,0.0on other static targets

Bool: false

As a consequence, the Haxe Compiler does not allow the assignment ofnullto a basic type

on static targets. In order to achieve this, the basic type has to be wrapped asNull<T>:

1 // error on static platforms

2 var a:Int = null;

3 var b:Null<Int>=null; // allowed

Similarly, basic types cannot be compared tonullunless wrapped:

1 var a : Int = 0;

2 // error on static platforms

3 if( a == null ) { ... }

4 var b : Null<Int> = 0;

5 if( b != null ) { ... } // allowed

This restriction extends to all situations where unification (3.5) is performed.

Type:Null<T>

On static targets the typesNull<Int>,Null<Float>andNull<Bool>can be used to

allownullas a value. On dynamic targets this has no effect.Null<T>can also be used with

other types in order to document thatnullis an allowed value.

If anull-value is “hidden” inNull<T>orDynamicand assigned to a basic type, the default

value is used: