duck!

[Leandro Lucarella]

Michel Fortin, el 16 de octubre a las 18:19 me escribiste:
> On 2010-10-16 17:45:56 -0400, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> said:
> 
> >unittest
> >{
> >     auto x = new Drawable;
> >     auto a = nameone!Widget(x); // works
> >     //auto b = nameone!ColoredWidget(x); // doesn't compile
> >     auto c = nametwo!ColoredWidget(x);
> >     c.draw(); // works
> >     c.setColor(red); // throws NotImplemented during runtime
> >}
> >
> >"nameone" implements Kenji's current code. "nametwo" is the looser
> >form of duck typing: whatever methods match will work, and the
> >rest are implemented to throw during runtime.
> 
> What you're proposing above is just useless, and I'm honestly quite
> surprised you don't realize that.
> 
> The real duck type almost already exists in Phobos, and it's called
> a variant. The only problem with it is that it is powerless when it
> comes to calling functions without casting it's content to a type
> first. Make it so this code can run and then you'll have implemented
> duck typing for real:
> 
> 	class Duck { void quack(); }
> 	Variant v = new Duck;
> 	v.quack();
> 
> Well, mostly. It could also be argued that this too should work too:
> 
> 	Variant v = cast(Object)(new Duck);
> 	v.quack();
> 
> but that'd require runtime reflexion as part of ClassInfo.

I agree that "nametwo" is useless, but what you're proposing is plain
dynamic typing, not duck typing. Duck-typing is what Go (and adaptTo)
does. In dynamic languages you have to check for the methods existence
at runtime just because is the only way to do it, but if you want to use
a duck, you *need* to know that the object you're working with *can*
quack().

That doesn't make dynamic typing a bad idea, it can be useful, but
please don't name it "ducktype" as Andrei suggested.

-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
----------------------------------------------------------------------
GPG Key: 5F5A8D05 (F8CD F9A7 BF00 5431 4145  104C 949E BFB6 5F5A 8D05)
----------------------------------------------------------------------
Sometimes I think the sure sign that life exists elsewhere in the universe
Is that that none of them tried to contact us