Interface file

[Jan Johansson via Digitalmars-d]

On Wednesday, 30 September 2015 at 18:01:57 UTC, Adam D. Ruppe 
wrote:
> On Wednesday, 30 September 2015 at 17:51:50 UTC, Jan Johansson 
> wrote:
>> The interface file (I called it test.di):
>
> FYI there's no actual difference between .di files and .d 
> files. The way D is meant to be used is you write the 
> declarations together, then if you want to, you can 
> automatically strip the bodies out of a .d file (dmd -H does 
> it) and that makes the .di file.
>
>
> But you always substitute the .di file for the .d file with the 
> same name. They cannot be used together like a .h and .cpp file.
>
>
> You can put an interface in a separate module than a class. 
> Then you import the interface module from both locations, 
> though your factory function won't work like that.
>
> Try something like:
>
> itest.d:
>
> module itest;
> interface IMyTest {
>   void Write(string message);
> }
>
> test.d:
>
> public import itest; // import the interface definition too
> import std.stdio;
>
> private class MyTest : IMyTest {
>     void Write(string message) {
>         writeln(message);
>     }
> }
>
> public IMyTest createInstance() {
>     return new MyTest;
> }
>
>
>
> main.d:
>
> import test;
> import std.stdio;
>
>  void main() {
>      auto p = createInstance();
>      p.Write("Hello, World!");
>  }
>
>
>
> And that should work.
>
>>   dmd test.d test.di -lib -oftest
>
> would be more like `dmd itest.d test.d -lib -oftest`
>
>>   dmd main.d test.di test.a
>
> and `dmd main.d itest.d test.a`
>
>
>
> Or you could just compile it all at once with `dmd main.d 
> test.d itest.d`

Thanks,

But (there is always a but) ;-)

The main.d should rely on itest.d, not test.d, otherwise I do the 
declaration for the library itself, but the main.d includes the 
test.d - the implementation (not the declaration).

If I change the 'dmd main.d test.d test.a' to 'dmd main.d itest.d 
test.a', then I got a new error: itest.d:(.text._Dmain+0x5): 
undefined reference to `_D5itest14createInstanceFZC5itest7IMyTest'

The linker get confused about the separation of the declaration 
and implementation.

Best regards
Jan Johansson