Issue with forward ranges which are reference types

[Lars T. Kyllingstad]

On Wed, 17 Aug 2011 10:19:31 -0400, Steven Schveighoffer wrote:

> On Wed, 17 Aug 2011 00:05:54 -0400, Jonathan M Davis
> <jmdavisProg at gmx.com> wrote:
> 
>> So, the question is, should a range-based function have the same
>> behavior for
>> all forward ranges regardless of whether they're value types or
>> reference types? Or should the caller be aware of whether a range is a
>> value type or a
>> reference type and call save if necessary? Or should the caller just
>> always
>> call save when passing a forward range to a function?
>>
>>
> Probably not helpful, since the establishment seems to be set in their
> opinions, but I'd recommend saying ranges are always structs, and get
> rid of the save concept, replacing it with an enum solution.  The
> current save regime is a fallacy, because it's not enforced.  It's as
> bad as c++ const.
> 
> At the very least, let's wait until someone actually comes up with a
> valid use case for reference-based forward ranges before changing any
> code.  So far, all I've seen is boilerplate *RangeObject, no real
> usages.

As long as most functions in std.algorithm don't take the ranges as ref 
arguments, you need to use a reference-based range whenever you want the 
function to consume the original range.

BTW, this is why I suggested earlier that we add a byRef range.  If you 
absolutely want the function foo() to consume your range, write

   foo(byRef(myRange));

If you absolutely *don't* want the function to consume your range, write

   foo(myRange.save);

If you don't intend to use the range afterwards, and therefore don't care 
whether it is consumed or not, write

  foo(myRange);

-Lars