what's the point of function template declarations if they can't be defined?

[Marc]

On Thursday, 8 February 2018 at 07:21:05 UTC, Jonathan M Davis 
wrote:
> On Wednesday, February 07, 2018 13:39:55 Timothee Cour via 
> Digitalmars-d- learn wrote:
>> [...]
>
> It's useful with stuff like version(Ddoc).
>
>> [...]
>

What's a di file? (sorry google didn't help with that)
> It's been my understanding that it's always been illegal to 
> provide a definition for a function that was declared 
> previously unless it was declared in a .di file, in which case, 
> you're not really both declaring and defining it, but the .d 
> file is used when the module is compiled, and the .di file is 
> used by other modules which use that module, so the declaration 
> and definition are not seen by the same run of the compiler.
>
> - Jonathan M Davis