Re: [Foo new] vs [[Foo alloc] init]:
Re: [Foo new] vs [[Foo alloc] init]:
- Subject: Re: [Foo new] vs [[Foo alloc] init]:
- From: Gregory Weston <email@hidden>
- Date: Sun, 17 Feb 2008 17:28:49 -0500
On Feb 17, 2008, at 3:06 PM, Bill Bumgarner wrote:
On Feb 17, 2008, at 11:15 AM, Gregory Weston wrote:
See what you're saying? +alloc *or* +allocWithZone:.
See the subject? +alloc. It does not say anything about
+allocWithZone:.
See this code?
@interface MyTest : NSObject
@end
@implementation MyTest
+ (id)alloc
{
NSLog(@"allocating");
return [super alloc];
}
@end
You would have to override +allocWithZone: to have any kind of
reliable behavior.
Or you could just not assume that something which hasn't been
explicitly stated in the docs is guaranteed. That's what I've been
trying to say: The only promise the documentation makes about new,
alloc and allocWithZone is that they're peers. It doesn't say a peep
about any of them invoking any of the others to achieve that
equivalence. That lack of explicit promise - the utter inability to
make such a promise in general - is why it's wrong to say without a
whole lot of caveats that one technique is precisely equivalent to
another. Looking at the implementation of a method, rather than the
interface, as it exists today and saying "you can count on this" is
an outright rejection of one of the core concepts of OO.
+alloc is a cover for +allocWithZone: with a NULL zone. Not that
you would know that from the documentation, unfortunately.
Which means, like the current behavior of new, that's an
implementation detail that shouldn't really be relied on.
Without assuming anything, you would have to override both
allocator methods; +alloc and +allocWithZone:.
So what you're saying is that [Foo new] isn't actually reliably
equivalent to [[Foo alloc] init]? That all we can really assume about
the default implementation of +new is that it performs behavior
functionally equivalent to that performed by the default +alloc (and
then invokes init)?
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