"IndexType" for ranges

[Jonathan M Davis]

On Tuesday, October 02, 2012 15:17:58 monarch_dodra wrote:
> You might think "just use typeof(length)" BUT:
> *you aren't even guaranteed that "typeof(length)" will be
> correct! Certain ranges, such as iota, will return a length
> usually of type uint, but be indexed with ulong... :/
> *Infinite ranges don't have length...

I'd argue that that's a bug in iota. iota's length even specifically returns 
_IndexType_.

It makes no sense for length, opIndex, or opSlice to vary in type at all. They 
should all use the same type (ideally size_t). The fact that it's not outright 
required to be size_t is bad enough (though IIRC iota had some good reasons 
for using ulong).

> These are not big changes I'm proposing, but they *may* break
> some existing ranges. Those ranges are arguably retarded, and
> these changes would enforce correctness, but they'd break none
> the less. I'd like some feedback if you think this trait is worth
> pushing?

Requiring that length, opIndex, and opSlice all use the same index type would 
be very much the right way to go IMHO. If that's done however, I don't know if 
we'll really need IndexType (though it may still be a good idea to add it).

In addition, I'd argue that they should require that they all be at least as 
large as size_t (ideally, they'd even have to be either size_t or ulong and 
that's it - no signed types allowed), but that may be too strict at this point 
given that it could break existing code that did stupid stuff like use int 
(which _way_ too many people seem inclined to do).

- Jonathan M Davis