**OOPS** Forgot to say: This is Objective-C!

What I'm trying to do is pass in a class's NAME into a parameter for a method call.

-(Game Object *)instanceCreate:(GameObject *)pGameObject atX:(int)pX Y:(int)pY{
GameObject *temp = [[ [pGameObject class] alloc] init];
temp.x = pX;
temp.y = pY;
return temp;
}

So basically I want it to accept the name of any GameObject object, or its subclasses and create an object of GameObject. So if I have bulletObject as a subclass of GameObject, I could pull of something like:
[self instanceCreate:bulletObject, 100, 100];
..and it will create a Bullet object to do whatever I want. It LOOKS like it's working okay, but during the GameObject's init, I define it "x" and "y" as properties. If I do the code in this manner, I get the error:
"Request for member 'x' in something not a structure or a union".

What does it need to look like to work? Thanks!

Do you mean you want to pass in a class, like instanceCreate:[Bullet class] or do you want to pass in an NSString with instanceCreate:@"Bullet" ?


or

While that second implementation yields no errors...

Still gives me those same errors after setting the x and y values. Why is this?

because "id" doesn't have properties called "x" and "y", like the error message says.

EVERY instance created will be a subclass of GameObject, which contains the "x" and "y" variables, but I want to allocate space for the class called into the parameter.

So how would I be able to set the X and Y values in this function, following the class allocation, since the object of type "id" doesn't contain these values?

Honestly it sounds like You're Doing This Wrong.

But if you use GameObject* instead of id, you'll tell the compiler that it's always a GameObject, and then you can use .x= and .y= if GameObject defines those as writable properties.

I am probably doing this wrong, but I like to find out the errors the hard way, I guess. It allows me to remember not to make them...!

Cool, so that works wonderfully. A couple more questions.
If I allocate an instance of, for example, the Bullet class such as this...


and Bullet is a child class of GameObject, will there be any problems when I want to find all the instances of "Bullet" in my game? Will it treat "temp" as a Bullet, or as a GameObject?

And:
I'd like to return a reference to temp, but when I change the return type from void to GameObject*, it's giving me a bunch of warnings:
"Expected ')' before 'GameObject' "

But I'm pretty sure my parenthesis are good... no?

Temp is statically a GameObject, which means the compiler will yell if you try to do something to it that you can't do to a GameObject. It's dynamically a Bullet, though, so if you (for example) send a message to it which GameObject declares and Bullet overrides, you'll get Bullet's implementation.

Just try it

SamBaylus Wrote:I'd like to return a reference to temp, but when I change the return type from void to GameObject*, it's giving me a bunch of warnings:
"Expected ')' before 'GameObject' "

But I'm pretty sure my parenthesis are good... no?

Yep, your parens are fine - you probably need to import GameObject.h into this file so that the compiler knows what a GameObject is. Then the error will go away.

Cookie, when you say "You're Doing This Wrong" I assume you mean you shouldn't be passing strings around and creating classes from them.

I wouldn't use something like this for saving and restoring game state, or while the game was running. I can see a case for this when creating levels or events based on a file, though; how else would you do that other than a giant switch statement? The switch statement is safer, but tedious to maintain.

smasher Wrote:...
Cookie, when you say "You're Doing This Wrong" I assume you mean you shouldn't be passing strings around and creating classes from them.

I wouldn't use something like this for saving and restoring game state, or while the game was running.
...

I actually AM using this while the game is running. Well. Sort of. In ANY instance, I want to be able to create another instance of another object during runtime. By using a define functions instead of a method call just to keep it nice and neat looking:
instanceCreate(instanceName, x, y);
I can pass in the instanceName as a string, and provide and x and y to start the object out, and it'll also call code for all the init values and whatnot. I'm sure there's a much better way of doing this, but like I said before; it's a learning process.

**ALSO** I did import GameObject, but strangely enough the error went away from I changed my import classes from my .h to my .m. I'm not sure why this is, but now it works perfectly without errors. Hmm.