Infinite BidirectionalRange?

[spir]

On Sun, 26 Dec 2010 00:36:26 +0000 (UTC)
Tomek Sowiński <just at ask.me> wrote:

> > <proposed>
> > 
> > A random-access range is a bidirectional range OR an infinite forward
> > range that offers the primitive opIndex.
> > 
> > </proposed>
> > 
> > I can't be sure whether the former should also provide the primitive
> > 'length'.  
> 
> I think so. If you got random access and know the end, you should also
> know how far is the end element. At least I can't think of a counter
> example.

Same for me. And that's why I think '$' should map to a length attribute or property, and not to a not-yet-implemented opDollar. Make 'length partially magic for that case. Simpler, and would work in 90% cases, since 'length' is the _de facto_ conventional D name.

> > That would make sense, but having the hasLength helper makes it also
> > feel like 'length' is an optional property of ranges.  
> 
> Length in general is an optional feature of ranges.
> 
> Taking a look back, I wonder if the notion RandomAccessRange is useful
> at all. Where elements are accessed randomly (e.g. sorting, viewing),
> one doesn't really need the thing to be a range. That suggests a loose
> feature rather than a place in hierarchy. Was hasRandomAccess and
> hasSafeRandomAccess considered? (the latter has random access and
> (length (x)or infinity))

I agree. Or, conversely, make structs/classes that implement random-access (opIndom+length) be automatically considered as input/forwar/bidi without having to overload with 6 additional methods. Anyway, rewriting the loops may be different for such random-access ranges.

Denis
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