The Phantom Returns

This is a bit of weird - and undocumented - behaviour.

When you write scripts in Game Maker, you can have them return a value by using the return statement, like so:

What value does the script return if you don't have any return statement, though? Does it always return true, or false, or maybe something else? I wanted to know, and I learned something surprising when I looked into it.

At first I thought the answer was that the script would always return false, but this rule didn't always hold. What's more, the return values I was getting were seemingly random and unpredictable.

Finally I discovered what was going on. A script returns the value of the most recent equation.

What does that mean exactly? Well, for example, a script containing only this line:

...will return 10. And, likewise:

...will return 20. Whatever the result of the most recent equation is becomes the return value!

This holds true for math operators like *=, +=, and so on. This:

...will return the square of argument0.

How bizarre! Even if you leave out the return statement, you will still get "phantom" return values... I guess this might be the cause of odd behaviour once in a while, so it's good to know about.

Until next time, happy coding!