struct inheritance need?

[Janderson]

Weed wrote:
> I should explain why it's important for me:
> 
> For example, I am making a matrix object(s)
> 
> It should be:
> - any size
> - with ability of making matrix instance of a given size in compile time.
> - ability of creating matrix instance in runtime.
> 
> I have decided to make it struct because I need to create matrix
> object in compile time. in real program I'll need matricies of
> variable size and 3х1, 3х3, 6х6, 3х6 sizes (and may be other).
> 
> I want to make matrix template and insert in it with mixin operator
> several structures of different sizes (and this structs are not store 
> his dimensions in each instance, of course: variables width and height 
> declared as invariant). By doing this I'll get several different 
> structures  (matrix_dynamic, matrix3x3, matrix6x6 etc)
> 
> question is how those matricies can interoperate? They does not have
> common parent (structures does not have inheritance) , so I can't
> make common function for matricies of different sizes opAdd for
> example, and have to do functions for all types of matricies.
> 
> How should I implement such a class In D properly?     
> It possible in C++, but I like some of the language D

The classical approach is to have "helper" template functions. 
Essentially:

void doOpearation(mymatrix)(...)
{

}


Note this is compiletime polymorphisms.

Now if you want to add runtime polymorphism it is impossible to get away 
from a cost.  You can use a wrapper class like so:

interface CommonMatrix
{
	operation()...
}

class PolymorphicMatrix(mymatrix) : CommonMatrix
{
	operation()...
}

You'll probably find though that PolymorphicMartix should be some higher 
level concept, like car, or entity.

The great thing about these techniques is that they give a whole load 
more power then just using inheritance alone because you can essentially 
attach many different behaviors to that struct.

I hope that was helpful.

-Joel