Object Memory Release Question

[tmekeel]

What is the difference between the Fraction *answer object and the origin object in these two code examples?
What I'm trying to figure out is where did I release (or was supposed to) release the *answer pointer?  Does releasing the myFract object in main take care of the pointer in the add method? I feel like I'm missing a fundamental point about memory allocations 
The origin object is created in the setOrigin method, so we have to deallocate it there as well, but why not [Fraction *answer]?

Code: (Objective-C)

-(Fraction *) add: (Fraction *) f
{
	//Tp add two fractions:
	// a/b +c/d = ((a * d)+(b * c)) / (b * d)
	Fraction *answer = [[Fraction alloc] init];
	
	answer.numerator = (numerator * f.denominator) + (denominator * f.numerator);
	answer.denominator = denominator * f.denominator;
	
	[answer reduce];
	return answer;
}

Code: (Objective-C)

-(void) setOrigin: (XYPoint *) pt
{
	if (origin)
		[origin release];
	
	origin = [[XYPoint alloc] init];
	
	[origin setX: pt.x andY: pt.y];
}

[skochan]

In the case of the Rectangle class, origin is an instance variable, so you have  a handle on the object and can therefore release it in the dealloc method.   In the case of the Fraction's add: method, the allocated fraction is not stored in an instance variable and is returned as the result of the addition.  Further, you may end up allocating many fractions if you add a lot of fractions.  Because of these reasons, a different approach is needed:  either each allocated fraction has to be released by the caller of the method (e.g., inside main) or else each fraction needs to be added to the autorelease pool by sending it an autorelease message (as discussed later in the text), so it will be released when the autorelease pool gets drained.

Cheers,

Steve Kochan

[tmekeel]

Thanks Steve