Question

If I allocate an object in a method, ‘getASprocket’ and call it this way, will there be a leak here?

Sprocket *sprock = [Sprocket getASprocket];

// store this returned value as an ivar
ivarSprock = [sprock retain];

// release the originally acquired object
[sprock release];

The Sprocket object is allocated and returned this way:

– (Sprocket *)getASprocket {
    Sprocket *sprocket;

    sprocket = [[Sprocket alloc] init];

    return [sprocket retain];
}

Also, would changing from '[sprocket retain];' inside the ‘aSprocket’ method to 'return [sprocket autorelease];' make worse performance hit?

Answer 1

Please see this good explanation page Especially sub-page #7

each retain created another memory object. so lets see what we’ve got:

in getASprocket :

sprocket = [[Sprocket alloc] init];

+1

return [sprocket retain];

+1

and on your method:

ivarSprock = [sprock retain];

+1

[sprock release];

-1

What should we do?
Well we should let the Sprock go by making it autorelease:

  return [[[Sprocket alloc] init] autorelease]

or in the words of the reffered link above:

In most cases, the setter for an instance variable should just autorelease the old object, and retain the new one. You then just make sure to release it in dealloc as well.