[cfe-dev] Adding namespaces to Objective-C

[Jens Ayton]

Ariel V Feinerman:
> 
> Jens,
> 
> do you mean?
> 
> @interface MyClass : NSObject {
> 
> }
> @namespace ns
> - method;
> @end
> 
> @namespace my
> - method;
> @end
> 
> // global
> @namespace 
> - method;
> @end

Something along those lines, yes.

The methods could then be called as:

[foo ns method];
[foo my method];
[foo method];

If the last one wasn’t there, you could of course use an @using directive or similar to avoid the explicit namespace.

As for duck typing, which someone mentioned: the point is to partition selectors into non-overlapping sets. Calling [foo my method] could never resolve to a call to [foo method] any more than [foo my_method] would. The difference is that you can use @using to dispense with the explicit namespace. (Namespace resolution would be based on the static type of a variable, and not apply to id values.) On the other hand, if foo is, at runtime, of a different class with a “my method”, that would be called.

Selector expressions would always take an explicit namespace, as in @selector(my method). Ideally, there would be no mangling; SELs would simply contain/reference strings with a single space as a separator. (This also means sel_getName() wouldn’t need to do any processing.)


Preferably, the namespace identifier would be separated from the true name; the identifier needs only be unique at compile time, while the true name disambiguates at runtime.

@interface NSDictionary (JAUtilities)
@namespace se.jens.ayton.JAUtilities as jautil // Applies to end of @interface scope if not changed.

- (NSString *)stringForKey:(id)key;

@end

...
// These all call the same method.
NSDictionary *dict = whatever;
string = [dict jautil stringForKey:key];

@using jautil;
string2 = [dict stringForKey:key2];

string3 = [dict performSelector:@selector(jautil stringForKey:) object:key3];

string4 = [dict performSelector:NSSelectorFromString(@"se.jens.ayton.JAUtilities stringForKey:") object:key4];



NSDictionary *fake = [NSString string];
[fake jautil stringForKey:@"foo"];
// Runtime error: NSString does not respond to "se.jens.ayton.JAUtilities stringForKey:"



Incidentally, this was loosely inspired by ECMAScript 4th Edition, may it rest in peace and at length.

-- 
Jens Ayton