On Feb 16, 2008, at 12:11 PM, Bill Bumgarner wrote:
On Feb 16, 2008, at 4:56 AM, Gregory Weston wrote:
Without that guarantee, there's a different between saying "this
statement accurately describes all current implementations" and
"this statement is correct." It is not correct in general to say
that "[Foo new] is exactly equivalent to [[Foo alloc] init]."
Those are the kind of assumptions that burn you after you've
forgotten you made them in the first place.
In general, I agree. In this particular case, I'm not concerned.
If Apple were to change the implementation of +new to *not* do
+alloc followed by -init, many many bits of code would break.
Binary compatibility between release of Mac OS X is critical and,
thus, this particular behavior cannot change.
I'm afraid I don't understand that assertion at all. What does this
have to do with binary compatibility? Why did it *not* break
compatibility in the move from 10.4 (in which new does not invoke
alloc by default) to 10.5 (in which it does)?
Reading the docs, it explicitly states:
...
This method is a combination of alloc and init. Like alloc, it
initializes the isa instance variable of the new object so it
points to the class data structure. It then invokes the init method
to complete the initialization process.
...
From there, the documentation entirely discusses implementing
+new... as a cover for various -initWith... style initializers.
Thus, the bare behavior of +new is quite thoroughly well defined as
a combination of +alloc and -init (in the docs, the the two method
names are links to the documentation of said methods).
It's well defined as being functionally equivalent by default to
alloc and init. It is even defined, as I had already noted, as
invoking init specifically. Given that explicitness, I would argue
that it's likely meaningful that the documentation does *not*
explicitly indicate that it invokes alloc. In fact the implication of
"Like alloc, ..." is very strongly that it's only guaranteed to be an
equivalent, not a wrapper. And since any developer who wants can
override alloc and new at any time they like, even though Apple
*does* implement new to invoke alloc by default it cannot be reliably
said to do so.
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