RefRange

[Jonathan M Davis]

On Thursday, June 14, 2012 07:35:35 Lars T. Kyllingstad wrote:
> On Thursday, 14 June 2012 at 04:14:02 UTC, Jonathan M Davis wrote:
> > I ran into a situation where I needed a forward range which was
> > not a
> > reference type to be consumed by a range-based function. Input
> > ranges and
> > reference type forward ranges are automatically and unavoidably
> > consumed by
> > range-based functions (assuming that save isn't called on them
> > before the
> > function starts consuming them), but that doesn't happen for
> > either value type
> > ranges or arrays. Hence my wrapper type (called RefRange). The
> > code is here:
> > 
> > http://codepad.org/nNB4mAdN
> > 
> > I was wondering what other people's take on it was and whether
> > I missed
> > something which makes it a bad idea. Essentially, it's a range
> > with a pointer
> > to the original range so that any function calls on the wrapper
> > affect the
> > original range (and vice versa).
> > 
> > Assuming that no one pokes a major hole in it, and others think
> > that it's a
> > worthwhile addition, I'll create a pull request for it to be
> > added to
> > std.range. But I'd like other people's feedback on it first.
> 
> It is definitely a good idea.  Basically, it provides the
> opposite guarantee of save().  If you're going to use the range
> once and then throw it away, and therefore don't care whether it
> is consumed or not, just use it directly.  If you want to ensure
> it does not get consumed, use a copy obtained through save().  If
> you want to ensure it *does* get consumed, use a reference to it.
> 
> However, someone pointed out here earlier that, since D uses the
> dot operator for pointer dereferencing, a pointer to a range is
> also a range.  It just isn't recognised as such by foreach.  So
> if we could just fix foreach, and maybe add functions providing
> range primitives for T[]* to std.array, I don't think we need a
> separate RefRange.  Just take the address of the range when you
> want to ensure it gets consumed.

I don't think that that would work with save or opSlice though. Granted, save 
and opSlice _can_ make it so that the range isn't consumed like you'd like, 
depending on how the function that you're passing it to is implemented, but 
having RefRange implement save and opSlice is still useful, and is actually 
necessary if you want it to work as RandomAccessRange and the like (since all 
of the more complex ranges are forward ranges). So, if that won't work with a 
pointer (and I don't think that it will, since the type would be completely 
wrong), then you'd still need a type like RefRange.

- Jonathan M Davis