Macromedia flex 2-migrating applications to flex 2 User Manual

Typing

33

Type detection

To perform type detection, you should use 

is

 rather than 

typeof

 or 

instanceof

. The 

is

 

function examines types, whereas the 

instanceof

 function looks at the prototype chain. The 

instanceof

 function has been deprecated. 

For example:

class B {

public function B() {}

}

class A extends B {

public function A() {

super(); 

}

}

class Main extends MovieClip {

public function Main() {

var a:A = new A();
trace(a instanceof B); // false; instanceof is deprecated.
trace(a instanceof A); // false; instanceof is deprecated.
trace(a is B); // true
trace(a is A); // true

}

}

Primitive types

In ActionScript 3.0, there is no longer a distinction between primitive types such as strings 
and instances of the String class. All strings are instances of String; every datatype is an 
instance of some class. The same is true for numbers and Booleans. For example:

print("test" == String("test"));

// true 

print("test" === String("test"));

// true

print(45 == new Number(45));

// true 

print(45 === new Number(45));

// true

print("one;two;three".substring(4,7)); // "two"
print((255).toString(16));

// "ff"

Non-assignment expressions

A non-assignment expression is any expression where a value is not assigned to a property (or 
a variable or argument); for example:

var myVar : hintString ? String : Number;