On Feb 18, 2008, at 6:53 AM, Gregory Weston wrote:
On Feb 17, 2008, at 6:05 PM, Bill Bumgarner wrote:
If you are overriding +alloc for whatever reason, you better had
override +allocWithZone:, too.
The real point is that there's no formal requirement that you do
so. It only becomes an issue if you make unwarranted assumptions
about the implementation.
If you're familiar with Cocoa, you know that the documentation is
somewhat lacking. That sucks, but on this particular point the
documentation seems reasonably clear. The Discussion for alloc
begins as follows:
"The isa instance variable of the new instance is initialized to a
data structure that describes the class; memory for all other
instance variables is set to 0. The new instance is allocated from
the default zone—use allocWithZone: to specify a particular zone."
Ok, it even mentions allocWithZone: right at the beginning, so let's
read its Discussion:
"The isa instance variable of the new instance is initialized to a
data structure that describes the class; memory for its other
instance variables is set to 0. If zone is nil, the new instance will
be allocated from the default zone (as returned by
NSDefaultMallocZone)."
Now, it's not stated exactly and formally, but if you're familiar
with Cocoa, you know that it's an extremely common pattern to have
methods doSomething and doSomethingWithArgument:, where doSomething
is implemented as doSomethingWithArgument:nil. Thus, if you're
familiar with Cocoa, your first thought after reading those
Discussions above is that maybe alloc is implemented as
allocWithZone:nil.
And if you're not familiar with Cocoa, it's not the greatest idea to
override such a crucial method as alloc.
-Jeff
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