Re: [boost] difference_type size()?

Subject: Re: [boost] difference_type size()?
From: Olaf van der Spek (ml_at_[hidden])
Date: 2011-10-19 15:21:00

On Wed, Oct 19, 2011 at 8:50 PM, Jeffrey Lee Hellrung, Jr.
<jeffrey.hellrung_at_[hidden]> wrote:
>> I too stumbled upon this more than once. The common understanding of a
>> valid
>> range is that end() must be reachable by incrementing begin() finite times.
>> Making the size signed makes little sense to me and it also introduces a
>> problem (rather theoretical, however) when iterator_range is constructed
>> from
>> a very large valid range, whose size exceeds
>> numeric_limits<difference_type>::max().
>>
>
> How would that be possible?  Doesn't that violate the conditions on
> difference_type that it is able to represent the (signed) distance between
> any two iterators within the same range?
>
> Also, assuming that size() should return an unsigned integer type (I'm not
> debating the merits of this), *what* unsigned integer type should that be?

How about using make_unsigned from type_traits?

> I don't know of any general way to go from difference_type to a "compatible"
> unsigned integer type.  I suspect this will end up being filed away as "nice
> to have but ultimately unimplementable generically" given current range
> interfaces.

Isn't this problem caused by iterator_traits missing size_type?
What would the problem be of just using std::size_t?

-- 
Olaf