So, I think you can take nothing for granted. It always depends on the player..

Long vs Short variable names
This only applies to class-variables and parameter-variables as in
package
{
public class foo
{
private var bar:String;

private function fooBar(myLongVariableNameWillGetIntoHashTable:int = -1):void {}
}
}

All variables used inside methods are irrelevant, because these are transformed by the compiler, so they are not in a hash-table.

Multiplication vs. Division
Also notice that if dividing by 2, 4, 8, 16, etc. it is slight faster using bit-shift operators:
sprite.width = parent.width / 2;
would be:
sprite.width = parent.width >> 1;

Var declarations on multiple lines vs. Var declarations on a single line
I figured out that declaring multiple vars in a single line is faster when using the keyword var before every variable:
var i:int, j:int, k:int; //slower than
var i:int; var j:int; var k:int;

The problem is that it’s hard to read such code. I’m currently working on a Obfuscator that will also do some code-improvements.
I like the version of writing
var[TAB]i:int,
[TAB]j:int,
[TAB]k:int;
So you have all variables well-formatted :)

And one last additional hint:
When using class-variable, it’s faster accessible by using the this-keyword:
private var foo:String = ‘hello world’;

function bar():void
{
trace(foo); //is very slow
trace(this.foo); //is much faster
}

This is because the JIT has too look where the declared variable exists. If using this, the JIT knows that foo is a class-variable, otherwise it could also be a method-variable.

Kind Regards,
Daniel Bunte

I’m curious to know if the first point on Array.push () and Array.length is applicable to the new Vector. data type in Flex 3.3 and FP10?