Cascading, variable mixins

[Slavisa Radic]

Hello Folks,

I would like to augment a mixin with another mixin, which gets augmented by another mixin...and so forth

The most important design goal is, how to pass a mixin as parameter and the class which gets augmented by the mixin does not has to import the mixin.

My overall-goal is to be able to extend functionality of a class from outside, without the need to touch the class itself (kind of inter-type-declaration).

I managed to pass a template as an alias parameter to the class which was going to be augmented. This class was able to mix it in.

Next i tried to do the same with the template which gets mixed in. I parameterized it with an alias-parameter, and used the parameter as mixin.

However, this doesn't work. In order to parameterize the template, I had to instantiate it. This instantiated template then could not get mixed in in the class, as it was no template-name any-more.

To illustrate this a little bit:
---------------------------
import std.stdio;

class A(alias T)
{
    mixin T;
}
-------------------------

module b;
import std.stdio;

template B(alias T)
{
    public void foo()
    {
        writefln("This is template-code from Template B");
    }

    mixin T;
}
-------------------------------------------------------------------

module b2;

template B2()
{
    public void bar()
    {

        writefln("And This is Code from a different Template, namely Template B2");
    }
}
--------------------------------
private import a;
private import b;
private import b2;

int main(char[][] args)
{
    A! ( B! (B2) ) a = new A! ( B! (B2) ) ();
    a.foo();
    a.bar();
    return 0;
}
--------------------------------------------

Compiling this will result in the following error:
a.d:5: mixin T is not a template

And it's true. It is really no template as it gets instantiated in the main-function. The problem is, how to parameterize B without instantiating it?

I would realy apreciate it If somebody would have a solution for this, as I need it for my Master-Thesis. So please do not post comments like "why should somebody do such stuff" - there are people - e.g. me ;-)