Re: Why can't I name a property `tag'?
Re: Why can't I name a property `tag'?
- Subject: Re: Why can't I name a property `tag'?
- From: Brian Stern <email@hidden>
- Date: Thu, 10 Jul 2008 14:17:25 -0400
On Jul 10, 2008, at 12:44 PM, Michael Ash wrote:
On Thu, Jul 10, 2008 at 9:49 AM, an0 <email@hidden> wrote:
Thanks. But isn't it annoying for XCode to pretend to know something
for sure while in fact it is just a wrong guess? At least the warning
is very misleading.
The warning isn't misleading at all. Xcode is not pretending anything.
It *does* know it for sure, it's just *wrong*. The warning then
appears because this wrong information causes other problems in the
code later on, due to a mismatched type.
The compiler definitely should complain if it has two methods with the
same name but different return types to choose from, and it doesn't
know which one is right. I've seen it happen many times. If it didn't
happen to you, it's because either it wasn't seeing one of them, or
because you found a compiler bug.
This is an inherent hazard of using the "id" type. For best results,
you should avoid using any method name which is already in use unless
your return type is compatible with the one already in use.
Mike
Actually this problem extends not only to return types but also
parameter types. So if one has a class like this:
@interface MyDocument : NSDocument{
}
- (id)initWithData:(int)inData;
@end
And you try to build one:
MyDocument* doc = [[MyDocument alloc] initWithData:0];
You will receive an error: "incompatible type for argument 1 of
'initWithData:";
The problem of course is that alloc returns an id and gcc's method
matching is finding a different declaration of initWithData in the
Cocoa headers for another class.
So I would add "For best results, you should avoid using any method
name that is already in use unless its return type and parameters are
identical with the already existing method."
Obviously there is some potential for new versions of Cocoa to add new
methods that conflict with your own methods.
--
Brian Stern
email@hidden
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