higher-order funcs for ranges (with usual interface)

[Torarin]

If you want to use an interface as a concept, you can take kenji's
adaptTo module and add this:

template conformsTo(T, Interfaces...)
{
 enum conformsTo = AdaptTo!Interfaces.hasRequiredMethods!T;
}

and use it like this

void draw(T)(T shape) if (conformsTo!(T, Shape, Drawable))

This will of course only work for methods, not properties or aliases,
so you still need constraints in some cases.

Torarin