Re: multiple declarations for method `length' ?

FROM : John Stiles
DATE : Thu Dec 30 19:36:27 2004

On Dec 30, 2004, at 10:16 AM, j o a r wrote:

> Please don't cross-post!
>
> 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…

>
> 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:
>
> NSString *str = [[NSUserDefaults standardUserDefaults] objectForKey:
> NSDecimalSeparator];
> short decimalLen = [str length];
>
> or
>
> short decimalLen = [(NSString *)[[NSUserDefaults standardUserDefaults]
> objectForKey:NSDecimalSeparator] length];
>
> j o a r


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.