Constraints

["İbrahim Gökhan]

> but for what then interfaces are?

Interfaces are for classes, and provides a virtual interface.
Concepts are for all, and provides a generic, static interface. 
Not to use as base class.

> but what concept should for example an array have? the 
> typecheck of the array itself???

For example CInputRange can be used for arrays, or other ranges 
that did not derived from CInputRange. It's only have some 
constraints.

> if your world is very OOPish orientated - but the generic world
> keeps itself away from "derived functionality"

Not derived functionality, derived constraints. When you derive a 
concept you only compose the constraints by AND logic.

> but the type should only satisfy the concept
> its does not need to derived from that - think of the thoundsand
> of specialised concept-classes that will occure (for example in 
> phobos)

You can use a different syntax instead of inheritance.
Simple things should be done by using template constraints. I did 
not offer to remove template constraints. So if you need an 
interface like Ranges you use concepts, if you don't need an 
interface you use template constraints.