"IndexType" for ranges

[Jonathan M Davis]

On Tuesday, October 02, 2012 18:45:50 Peter Alexander wrote:
> On Tuesday, 2 October 2012 at 16:29:28 UTC, Simen Kjaeraas wrote:
> > On 2012-10-02, 18:09, Peter Alexander wrote:
> >> On Tuesday, 2 October 2012 at 13:17:45 UTC, monarch_dodra
> >> 
> >> wrote:
> >>> If you've ever worked on a template that needs to index a
> >>> range, you may have run into this problem: What is the type
> >>> you should use to index an RA range?
> >> 
> >> Forgive my ignorance. What's wrong with size_t?
> > 
> > That not all ranges use it? If the range uses int, short, byte
> > (I wonder why they'd do it, though), using size_t will not even
> > compile.
> 
> That's kind of my point. Unless there's a compelling reason not
> to, I'd suggest we standardise on size_t indexing (and length)
> and avoid this issue altogether.
> 
> C++ containers have a size_type typedef. No one uses it.
> 
> Let's keep things simple instead of complicating things for the
> sake of unwanted "flexibility".

In general, all ranges _should_ use size_t for both length and indexing, but 
for a few range types in Phobos specifically use ulong (e.g. IIRC iota does in 
order to work properly with ranges or long and ulong on 32-bit systems). I see 
_zero_ reason to support lengths or indices smaller than size_t. Types that do 
that are badly designed IMHO. But we already have a precedent that you can't 
always assume size_t (at least for length - I'm not sure about indices - but 
if length can be specifically ulong and the type is random access, then its 
indices will need to be ulong), so unfortunately, the situation is not so 
simple that you can always assume size_t (even you should arguably be able 
to).

- Jonathan M Davis