Dithering about ranges

[Andrei Alexandrescu]

Georg Wrede wrote:
> Not cosidering D or programming, the notion of a range implies a 
> beginning and an end.

Actually, not. Infinity is a primitive notion with ranges. A range that 
defines empty like this:

enum bool empty = false;

is detected as infinite and treated accordingly by certain other ranges 
and algorithms. See isInfinite in std.range.

> So, in a certain sense, ranges could be 
> conceptualized as slices.

Yes, slices were a motivator and model for ranges.

> All's well, and everything. But, things like input streams don't really 
> support the notion of "range", or "slice". They don't even want to.

Why don't they?

> Sure, one could "coerce" or "forge" an input range to pretend some 
> manner of them, but that would be awkward at best, and laborios in 
> practice.

What would be a natural interface for an input range?

> Does that mean that I'm against ranges? No. But there might be the 
> possibility that ranges are not a panacea. Just as Structured 
> Programming wasn't (look at Walter's gotos all over the place), OOP 
> wasn't, Functional Programming wasn't, or that metaprogramming doesn't 
> tell us whether God exists. Ranges solve some gargantuan problems in 
> Modern Programming, but I don't expect them to usurp a dozen of other 
> paradigms.

For sure nobody cracked them to be that great. I think you perceive them 
as an imposition when they really are some rather unremarkable types 
with at most a handful of primitives.

> Could it be that the optimum would be to have /both/ ranges and, ehhh, 
> pointing notions?
> 
> Today, no sane programmer (outside of C or outside of Java) would make 
> his application /entirely/ ranges or /entirely/ classes.

I don't quite understand this. Ranges are a very simple abstraction for 
iteration. They show how other iteration abstractions either were too 
unsafe and verbose (C++/STL) or too bare-bones (C# iterators, Java 
iterators, singly-linked lists used by functional languages), so in that 
regard I think they hit the spot pretty nicely. Ranges are useful, but 
hardly a be-all end-all. Thinking of building an application entirely of 
ranges... I can't quite parse that.


Andrei