Question

In my program I have

NSString *stringOne = [NSString stringWithFormat:@"Hello World"];
[variable insertText:stringOne];

and the code runs fine. I know that the ‘stringWithFormat:’ method initiates the object, but where does the alloc happen? And why is it not needed here?

I can do the same with NSSound

NSSound *favoriteSong = [NSSound soundNamed:@"Friday"];
[favoriteSong play];

this will run, too. I know that ‘soundNamed:’ returns & initiates the object but the NSSound was never allocated.

I always assumed that I would have to do the following..

NSSound *favoriteSong = [[NSSound alloc]initWithBlablanla];

and then continue from there in order for everything to work.

What Im asking is, where does the allocate happen?

Answer 1

Some methods like soundNamed allocate an autoreleased object and return it. As an example, and let’s imagine those 2 methods exist :

calling :

NSSound *favoriteSong = [NSSound soundNamed:@"Friday"];

return a NSSound allocated object, inited with @”Friday”. This returned object is autoreleased.

calling :

NSSound *favoriteSong = [[NSSound alloc] initWithSoundNamed:@"Friday"];

return a NSSound allocated object, inited with @”Friday”. This returned object is retained, and must be deallocated.

Those two calls would do the same thing :

NSSound *favoriteSong = [NSSound soundNamed:@"Friday"];
NSSound *favoriteSong = [[[NSSound alloc] initWithSoundNamed:@"Friday"] autorelease];

As a shortcut, soundNamed is something like :

+ (id) soundNamed:(NSString*)name
{
    NSSound* aSound = [[NSSound alloc] initWithSoundNamed:name];
    if (!aSound) return nil;

    return [aSound autorelease];
}