Ranges

[Steve Teale]

Robert Fraser Wrote:

> Steve Teale wrote:
> > template isInputRange(R)
> > {
> >     enum bool isInputRange = is(typeof(
> >     {
> >         R r;             // can define a range object
> >         if (r.empty) {}  // can test for empty
> >         r.popFront;          // can invoke next
> >         auto h = r.front; // can get the front of the range
> >     }()));
> > }
> > 
> > I can not possibly be the only D enthusiast who finds this completely incomprehensible. 
> 
> Yeah, that one is a bit tricky, and what makes it worse is that it seems 
> officially sanctioned by Walter/Andrei as the "right way" to check if a 
> type supports some operations. Basically, if you have:
> 
> is(typeof({ @@@ }()));
> 
> this means "if I made a function containing @@@, would that function 
> compile?". It's a hack which stems from the way the is expression works.
> 
> > What is a range?
> 
> As others have mentioned, it's just a struct (or other type) that 
> happens to support certain operations.

So does this mean that interfaces are just a tragic mistake. I'd always thought that what you said was a pretty good description of what an interface is!