How to create a function declaration?

[Frits van Bommel]

Sean Kelly wrote:
> Frits van Bommel wrote:
>>
>> You're writing forward declarations. Seriously, D doesn't need them; 
>> forward references are allowed ;).
>>
>> A function declaration without definition is for when you put the 
>> definition in a different file, not to put it later in the same file.
> 
> I think the same conflict can occur in this situation though:
> 
>     module a;
> 
>     extern (C) void fn();
> 
>     module b;
> 
>     extern (C) void fn();
> 
>     module c;
> 
>     import a, b;
> 
>     void main()
>     {
>         fn();
>     }
> 
> This one has bitten me a few times where I had declared the prototype 
> for a C library routine to avoid importing the entire header module, and 
> a derived module imported both my module and the C header module.  Even 
> worse, the same error will occur if one of the two declarations is 
> private, because of how symbol resolution is handled.  This makes the 
> approach outlined above completely intractable, and actually more 
> restrictive than C where multiple prototypes of the same function are 
> allowed.

You cut that quote a bit short. Reread the rest of that paragraph at the 
end of your quote.
What I was talking about was more in the line of Phobos' object.d & 
internal/object.d, or a C source file and its D import module.
Either way, only one of the files is intended to be imported (but 
shouldn't get compiled itself). The other file then gets compiled and 
linked in its place.