Re: why does this method return an id?
Re: why does this method return an id?
- Subject: Re: why does this method return an id?
- From: Charles Srstka <email@hidden>
- Date: Sun, 11 Dec 2011 12:34:57 -0600
On Dec 11, 2011, at 10:58 AM, Matt Neuburg wrote:
> There seems to be a small hole in my understanding of Objective-C. I sort of understand why alloc-init returns an id, but why do so many class method convenience instantiators also return an id? For example:
>
> [NSSortDescriptor sortDescriptorWithKey:@"indexOrig" ascending:YES]
>
> That method is declared as returning an id, which means you can use it accidentally anywhere, assign the result to the wrong thing, and get a mysterious crash. (Guess how I know that?) Now, I think I know why [NSString string] is declared as returning an id - it's because it's a class cluster, right? But NSSortDescriptor isn't a class cluster; the result really is an NSSortDescriptor. So why isn't it *declared* as an NSSortDescriptor? Thx - m.
Most likely it’s to accommodate subclasses. If it weren’t declared to return an id, then doing something like this:
MyFancySortDescriptorSubclass *sortDescriptor = [MyFancySortDescriptorSubclass sortDescriptorWithKey:@“Foo” ascending:YES];
would cause a compiler warning.
Charles_______________________________________________
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