protocol for using InputRanges

[Andrei Alexandrescu]

On 3/26/14, 8:37 AM, Steven Schveighoffer wrote:
> On Wed, 26 Mar 2014 11:09:04 -0400, Regan Heath <regan at netmail.co.nz>
> wrote:
>
>> On Wed, 26 Mar 2014 12:30:53 -0000, Steven Schveighoffer
>> <schveiguy at yahoo.com> wrote:
>>
>>> Gah, I didn't cut out the right rules. I meant the two rules that
>>> empty must be called before others. Those are not necessary.
>>
>> I see.  I was thinking we ought to make empty mandatory to give more
>> guaranteed structure for range implementors, so lazy initialisation
>> can be done in one place only, etc etc.
>
> Yes, but when you know that empty is going to return false, there isn't
> any logical reason to call it. It is an awkward requirement.
>
> I had the same thinking as you, why pay for an extra check for all 3
> calls? But there was already evidence that people were avoiding empty.

I think requiring users to call empty before front on input ranges is a 
concession we should make.

Andrei