Question

I would like to know what’s the difference when I write a temporary variable like this (these are just examples):

version1

for each tempEnemy in enemyManager.enemies {
var tempX:int = tempEnemy.x;
}

or this:

version2

for each tempEnemy in enemyManager.enemies {
tempEnemy.oldX = tempEnemy.x;
}

What’s wrong and right? Currently I write it like version 2 and I’m not sure if I should change it to version 1. Can someone help me out with this please? I know most developers write like version 1 but I’m a little bit confused because I am totally unaware about version 1. If I use version 1 does that mean that my value is stored explicitly in a temporary variable that is cleared in every cycle?

Answer 1

In version 1 the declaration:

var tempX:int

defines a variable that lasts only as long as that iteration of the for (or for-each) loop it’s in. Each iteration tempX is defined, given a value from an Enemy object, and at the end it is left for garbage collection.

In version 2, you reference two variables attached to an Enemy object referenced by the temporary variable named tempEnemy.

In both versions the reference to the Enemy object, tempEnemy, is reassigned the next iteration’s Enemy object.

Each method has its advantages. From a memory standpoint, version 2 is probably better, since it changes an existing variable over and over rather than creating a new variable that’s discarded at the end of each iteration. On the other hand, version 1 doesn’t require you to have oldX defined in its class variables, which can often get mucky enough without these sorts of variables.

Best practices with code are based off of (a) working with other programmers, who need to be able to read and understand the code, and (b) leaving a project and coming back to it later, where you’ll need to be able to read and understand your own code. For short projects you don’t plan on sharing, version 2 is okay (and probably more memory-efficient), but any large project should use something more like version 1.

Another consideration is, are you going to use that variable anywhere other than the function where it is defined(set)? If not, you don’t need to store it in the object, which points again to version 1.