casting & templates

[Chris Wright via Digitalmars-d-learn]

On Sun, 31 Jan 2016 19:59:01 +0100, Robert M. Münch wrote:

> I have:
> 
> class OperatorV(T) : Value {
>   T impl;
> 
>   this(T impl) {
>     this.impl = impl;
>   }
> ...

This expands to:

template OperatorV(T) {
  class OperatorV {
    ...
  }
}

If you're just typing `OperatorV` with no template arguments, you're 
referring to the template itself.

There's not necessarily any relationship between two instantiations of a 
template with different arguments. You could write it so that OperatorV!
int and OperatorV!string have entirely different sets of methods, 
constructors, and fields.

Because of that, the compiler doesn't create a base class for you 
automatically. But you can do it yourself:

class BaseOperator {}  // or interface, or abstract class
class OperatorV(T) : BaseOperator {}