Conditionally change the direction of a "for loop"? - actionscript-3

Question

Is it possible to conditionally change the direction of a for loop in ActionScript?
Example:
for(if(condition){var x = 0; x<number; x++}else{var x=number; x>0; x--}){
//do something
}

Answer 1

Interesting requirement. One way to keep the for is:
var start, loop_cond, inc;
if(condition)
{
start = 0;
inc = 1;
loop_cond = function(){return x < number};
}
else
{
start = number - 1;
inc = -1;
loop_cond = function(){return x >= 0};
}
for(var x = start; loop_cond(); x += inc)
{
// do something
}
We setup the start value, a function for the termination condition, and either a positive or negative increment. Then, we just call the function and use += to the do the increment or decrement.

Answer 2

ActionScript has the ternary operator, so you could do something like:
for (var x = cond ? 0 : number; cond ? x < number : x > 0; cond ? x++ : x--) {
}
But this is pretty ugly. :-)
You might also need/want to put some parens around pieces of that. I'm not sure about the operator precedence.
You might also consider using a higher order function. Imagine you have:
function forward (count, func) {
for (var x = 0; x < count; x++) {
func(x);
}
}
function backward (count, func) {
for (var x = count - 1; x >= 0; x--) {
func(x);
}
}
Then you could do:
(condition ? forward : backward) (number, function (x) {
// Your loop code goes here
})

Answer 3

You probably want a while loop instead:
var continueLooping, x;
if(condition)
{
x = 0
continueLooping = (x < number);
}
else
{
x = number;
continueLooping = (x > 0);
}
while (continueLooping)
{
// do something
if(condition)
{
x++;
continueLooping = (x < number);
}
else
{
x--;
continueLooping = (x > 0);
}
}
If you really want a for loop, you should use two of them:
function doSomething()
{
//doSomething
}
if(condition)
{
for(var x = 0; x<number; x++)
{
doSomething(x);
}
}
else
{
for(var x=number; x>0; x--})
{
doSomething(x);
}
}