three little tricks

Here are a couple of tricks I learned form this article:

I try never to access an array's length in a for loop:

for ( var i : int = 0; i < people.length; i++ ) ...

That's bad, because each time the loop iterates, it has to dig into people and access its length property. I get a boost in optimization (without losing clarity) by doing this:

var numPeople : int = people.length;
for ( var i : int = 0; i < numPeople; i++ ) ...

But I'm bothered by the fact that both i and numPeople are throw-away variables (just needed for loop mechanics), yet only one is declared outside the for statement. So here's the trick:

for ( var i : int = 0, numPeople = people.length; i < numPeople; i++ ) ...

I advocate either that or this:

var i : int = 0;
var numPeople : int = people.length;
for ( i; i < numPeople; i++ ) ...

Note: you could also write the for loop this way:

for ( ; i < numPeople ; i++ )...

Trick two:

Let's say you need to loop backwards through an array by index. You could do this:

var arr : Array = [ 10, 20, 30, 40, 50 ];
for ( var i : int = arr.length - 1; i <= 0; i-- )
{
trace( arr[ i ] );
}

//output: 50, 40, 30, 20, 10

or (here's the trick) you could just do this:

var arr : Array = [ 10, 20, 30, 40, 50 ];
var i : int = arr.length - 1;
while( i-- )
{
trace( arr[ i ] );
}

//output: 50, 40, 30, 20, 10

Why does that work? Won't i keep decrementing past zero (-1, -2, -3...)? No, because in the Boolean sense, zero reads as false (all other numbers read as true). So while( 0 ) will stop the loop.

One final trick:

I didn't learn this one from the article I liked to above. I've seen it in various places.

Let's say you want to either set a variable equal to a value read in from an xml file OR, if there is no value in the xml file, you want to set the variable to some default value. (Hint: note the word "or" in the previous sentence.)

Here's what I used to do:

if ( valueFromFile == null ) speed = valueFromFile;
else speed = 10;

or I might have done this:

speed = ( valueFromFile == null ) ? valueFromFile : 10;

or even this:

speed = ( valueFromFile ) ? valueFromFile : 10;

What I hate about all those versions is the stuttering of "valueFromFile." Via the trick, I can eliminate it like so:

speed = valueFromFile || 10;

I love how clean this looks, especially when you're using it with multiple values:

var speed : int = speedFromFile || 10;
var color : uint = colorFromFike || 0xFF00FF;
var name : String = nameFromFile || "George";