D/Objective-C Preliminary Design

[Walter Bright]

Michel Fortin wrote:
> On 2010-11-03 13:55:35 -0400, Walter Bright <newshound2 at digitalmars.com> 
> said:
> 
>> Thanks for doing this!
> 
> You're welcome.
> 
> 
>> "To make Objective-C methods accessible to D programs, we need to map 
>> them to a D function name. This is acomplished by declaring a member 
>> function and giving it a selector:"
>>
>> Why not just make the D member function the selector name?
> 
> The primary reason is that selectors have a different syntax than D 
> identifiers (they often contain colons). We could add some sort of 
> mapping, converting colons to underscores for instance, but that's not 
> very clean and would be a little ugly. Let me show you why.
> 
> Because in Objective-C arguments are interleaved inside the multi-part 
> method name (the selector), it's deemed good there to have very 
> expressive names. For instance, key-value-observing in Cocoa use this 
> method selector:
> 
>     addObserver:forKeyPath:options:context:
> 
> When you call this method in Objective-C, it's done like this:
> 
>     [o addObserver:self forKeyPath:@"window.frame" option:0 context:nil];
> 
> Let's convert this in a D-compatible syntax by replacing colons by 
> underscores:
> 
>     o.addObserver_forKeyPath_options_context_(this, "window.frame", 0, 
> nil);
> 
> Now imagine a whole program with functions like this one. Would you want 
> to write a program like that? I'd surely like to hear other's opinions 
> on that subject, but to me it seems to be a better idea to provide 
> adapted function names.

How about a way to use . instead?

     o.addObserver.forKeyPath.options.context(this, "window.frame", 0, nil);

That would fit right in with, say, forKeyPath being a "member" of addObserver.



> Another reason is that it allows Objective-C objects to behave more like 
> normal D objects. Objective-C doesn't have overloading -- you can't have 
> two methods with the same selector -- so overloading requires some kind 
> of mapping between the selector and the D function name. And some 
> algorithms might expect overloading, so having this capability improves 
> interoperability. But this is more like a secondary benefit.

I would say, for extern(Objective-C) functions, simply disallow overloading.