Cast vs as operator

I was wondering what's the difference between different types of casting. So I made some tests

var test1:Number;
trace( test1 as String); trace( test1.toString()); trace( String(test1));

//Output:
//null
//NaN
//NaN

OK, so we have two types casting. While 'as' returns us not defined String type (casted value also was not defined), standard casting creates instance that tries to use data casted type

Let's try the opposite way. But this time on defined instance

var test2:String = '100';  
trace( test2 as Number); 
trace( Number(test2));

//Output:
//null
//100

Casting give us instance with data gathered from base class. But 'as' operator one more time returns null. I wondered how does it work. And I found. Check this example:

var test3:Sprite = new Sprite(); 
trace( test3 as DisplayObject); 
trace( test3 as MovieClip);

Operator 'as' is concatenation of checking type of data and casting data. It casts only when base type is descendant of casted type. If expression is inherits casted class then it's returned. Otherwise it returns null

From String to Boolean - casting problem

This is not a great discover, but sometimes it can help to save some time while wondering why there is true when should be false. I usually meet this situation while reading data from url GET parameters or from XML.

Let's check the example:



var stringTrue:String = 'true';
var stringFalse:String = 'false';


var boolDataTrue = new Boolean(stringTrue);
trace('#1 String true is casted to:', boolDataTrue);
//#1 String true is casted to: true


var boolDataFalse = new Boolean(stringFalse);
trace('#1 String false is casted to:', boolDataFalse);
//#1 String false is casted to: true



For this example I made two variables. In Boolean constructor ther's object as argument. But no matter what kind of string you put there it always deals it as 'true' expression

For quick and short fix you have to put there expresion that checks text and returns true or false as a proper type:


var boolDataTrue = new Boolean(stringTrue == 'true'?true:false);
trace('#2 String true is casted to:', boolDataTrue);
//#2 String true is casted to: true


var boolDataTrue = new Boolean(stringFalse == 'true'?true:false);
trace('#2 String true is casted to:', boolDataTrue);
//#2 String true is casted to: false

Numerical attributes in XML & no value in code

I know it's a stupid case, but sometimes I forgot about simple things.

Problem:
we have numerical value in XML like:

<component itemHeight="20" itemsVSpace="10" .../>

in code we want to use those values

itemLabel.y = index*( _contentXML.@itemHeight + _contentXML.@itemsVSpace);

Result? We receive zero. Because attribute value is used as String and + works as concatenation. Then multiple converts value to zero. We have to cast values at the begining to expected type:

itemLabel.y = index*( int(_contentXML.@itemHeight) + int(_contentXML.@itemsVSpace) );