+[NSMutableArray array] returns a mutable array. That's the reason the
return type is + (id) and not + (NSArray *).
When implementing connivence initializers, you should invoke [self
alloc], not [ASpecificClass alloc]. Cocoa uses this pattern
frequently, and you can safely depend on it.
Objective-c classes are first class objects. That's a difference from
many other languages. Once you get uses to classes being first class
objects, and the fact that classes can have dynamic messages, this
becomes a lot more natural.
Good Luck -
Jon Hess
On Jan 9, 2009, at 5:45 PM, Kyle Sluder wrote:
On Fri, Jan 9, 2009 at 8:40 PM, Graham Cox <graham....@bigpond.com>
wrote:
Isn't guaranteed by the semantics of inheritance? I've specified
the class:
[NSMutableArray ... and what I want it to give me... array]; And
the fact
that NSMutableArray inherits NSArray ensures that anything that
array can
do, NSMutableArray can do.
No, it means that NSMutableArray responds to everything NSArray
responds to; there's no semantic guarantee. What if the subclass
needs a different designated initializer, maybe one with more
arguments? It would make sense for it to override the superclass's
designated initializer to throw an exception. But without overriding
the convenience constructor, this will blow up.
--Kyle Sluder
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