Interface file

[Jan Johansson via Digitalmars-d]

On Wednesday, 30 September 2015 at 17:51:50 UTC, Jan Johansson 
wrote:
> Hello all,
>
> I'm testing D language, and the first thing I want to do is to 
> separate declaration from implementation. I was happy to find 
> support of interfaces in the D language, and set out to do a 
> basic test. However, this test failed, and I want some newbie 
> help to understand how it should be done in D language.
>
> ----------------------
>
> The interface file (I called it test.di):
>
> // Interface
> interface IMyTest {
>   void Write(string message);
> }
>
> // Factory for type implementing IMyTest
> IMyTest createInstance();
>
> ----------------------
>
> The library file (I called it test.d):
>
> import std.stdio;
>
> class MyTest : IMyTest {
>     void Write(string message) {
>         writeln(message);
>     }
> }
>
> IMyTest createInstance() {
>     return new MyTest;
> }
>
> ----------------------
>
> And finally the main file (I called it main.d):
>
> import test;
> import std.stdio;
>
> void main() {
>     auto p = createInstance();
>     p.Write("Hello, World!");
> }
>
> ----------------------
>
> The assumption was that I could do:
>
>   dmd test.d test.di -lib -oftest
>
> and next do:
>
>   dmd main.d test.di test.a
>
>
> The shared information is in the test.di file.
>
> However, this failed, since the first statement generates the 
> following:
>
>   dmd test.d test.di -lib -oftest
>   Error: module test from file test.di conflicts with another 
> module test from file test.d
>
> I guess it is because the file name test.d and test.di creates 
> conflict, surfaced as module test.
>
> How can I accomplish what I want to do?
>
> Kind regards,
> Jan Johansson

Hi again,

Here is a re-worked example. Again, I want to use the factory 
pattern, and have created four files.

---

test.d (interface):

interface IMyTest
{
	void Write(string message);
}

---

mytesting.d (one implementation of interface):

import test;

class MyTesting : IMyTest {

     void Write(string message) {
         import std.stdio;
         writeln("MyTesting: " ~ message);
     }

}

---

factory.d (factory):

import test;
import mytesting;

IMyTest createInstance() {

     return new MyTesting;

}

---

main.d (program):

import factory;
import std.stdio;

void main() {
     auto p = createInstance();
     p.Write("Hello, World!");
}

---

There are a number of ways to build the executable.

I want to use binary linkage as much as possible (the next step 
is to do dynamically linkage - but here I need help - I'm still a 
newbie).

First I build the component (class) artifact:

   dmd mytesting.d -lib -ofmytesting

Next I build the factory artifact:

   dmd factory.d -lib -offactory

And then I close the loop:

   dmd main.d test.d factory.a mytesting.a

---

//Jan