UFCS for D

[Steven Schveighoffer]

On Fri, 30 Mar 2012 14:27:43 -0400, Walter Bright  
<newshound2 at digitalmars.com> wrote:

>
> I would argue that:
>
> 3. An extension method for an argument of type template parameter T will  
> be looked up only in the instantiation scope.

I don't think you looked at my counter case in detail.  Your idea leads to  
two different instantiations of tmpl!Foo having two different  
implementations, depending on which extension methods you include.  In  
fact, in one place, the instantiation might succeed, but in another, the  
instantiation might fail.

Given that the compiler simply trims out identically defined symbols,  
assuming they are the same, this could have disastrous consequences.  You  
could end up with code being different based on the link order, or  
possibly arbitrary decisions made by the linker!

My argument is that the one thing in common is that the module that  
defines the type has to have been included.  I think you would agree that  
the one truth we must maintain is that X!Y must be implemented exactly the  
same no matter what module instantiates it.

I realize that the compiler likely doesn't keep enough information to know  
what functions would fall under the rules I specified, so this is probably  
a difficult change to effect.  But it could be an incremental change later.

-Steve