extern(C) symbol conflicts

[Jonathan Marler via Digitalmars-d]

On Tuesday, 27 January 2015 at 18:13:36 UTC, Steven Schveighoffer 
wrote:e or the other, even though they are the same.
>
> I understand the idea behind keeping the lookup rules 
> consistent. But C lookup rules ARE simple.
>
> I would say if two extern(C) declarations are identical (i.e. 
> same parameter types, same attributes), they don't conflict. 
> What does this break?
>
> -Steve

This extern(C) thing is a bit odd.  With C, you can include as 
many headers and declare the same function as many times as you 
want to.  D is breaking this functionality.  However, some may 
see this as a feature.  Suppose you wanted to optimize where you 
were declaring your function prototypes by making sure there were 
no duplications?  In C, I can't think of a way to do this.  In D 
however, it looks like this would cause an error.

I kinda agree that maybe D should handle it the same way C does, 
but another thought comes to mind.  Say two libraries declared 
the same extern(C) function but they used different types or 
different type qualifiers.  You would have to go to one of the 
libraries and have them modify their's to be identical to the 
other right? Well, the difference now is that instead of them 
normalizing their declarations you can suggest that everyone use 
the same modules for declaring extern(C) functions.  This may 
have been impossible to do in an old language but since D is 
relatively new, this doesn't seem to unreasonable to do. Anyway, 
just some thoughts...I think this problem may be more complex 
then it seems.