Returning a pointer to memory allocated within a function in Cocoa Objective-C.

Question

In C, something like the following would be a disaster (ie, a memory leak) because you're returning a pointer to memory that you will never be able to free:

NSString* foo()
{
  return [NSString stringWithFormat:@"%i+%i=%i", 2, 2, 2+2];
}

Is that in fact totally fine in Objective-C since the memory that the returned pointer points to will be autoreleased? Even if it is OK, is it frowned upon for any reason? Any reason to prefer the C style, as below?

void foo(NSString ** modifyMe)
{
  *modifyMe = [NSString stringWithFormat:@"%i+%i=%i", 2, 2, 2+2];
}

Answer 1

Functions in Cocoa obey the same memory management rules as everything else in Cocoa. Your first example is perfectly fine.

Answer 2

Not only is it OK in Objective-C, but it’s not inherently a problem in C, as long as you have well-defined ownership semantics.

CFStringRef foo()
{
    return CFStringCreateWithFormat(NULL, CFSTR("%i+%i=%"), 2, 2, 2+2);
}

void bar()
{
    CFStringRef str = foo();
    CFRelease(str);
    // Nothing leaked.
}