Re: multiple declarations for method `length' ?
Re: multiple declarations for method `length' ?
- Subject: Re: multiple declarations for method `length' ?
- From: Charlton Wilbur <email@hidden>
- Date: Thu, 30 Dec 2004 13:57:55 -0500
On Dec 30, 2004, at 1:36 PM, John Stiles wrote:
On 2004-12-30, at 19.05, Mark Dawson wrote:
When compiling this Obj-C line in XCode 1.5, I get the following
warning:
LengthParser.m:295: warning: multiple declarations for method
`length'
short decimalLen = [[[NSUserDefaults standardUserDefaults]
objectForKey:NSDecimalSeparator] length];
What does this mean? It seems to run OK, producing the result (1
for US system) that I'd expect.
And Joar replies:
If you check NSDictionary you'll find that:
- (id)objectForKey:(id)aKey
...it returns an "id" object. In other words, the compiler don't know
what type of object it is. When you call the method "length" on that
object, the compiler needs to guess what implementation to use. If
there is only one such method it's easy, but if there are several
it's not. You can help the compiler by casting [...]
I thought one of the huge advantages of message-passing over function
calls was that you could send messages to "id" objects and objc_send
would sort out the details.
Yes, which is why it works. But the compiler, which is issuing the
warning, can't necessarily tell what value will receive the message at
runtime, and so it's warning you that there are two possible methods
that might be invoked depending on what class the object is. If you
want to get rid of the warning, you can make your intent clear to the
compiler by inserting a cast.
Charlton
--
Charlton Wilbur
email@hidden
email@hidden
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