Re: [boost] Re: Re: Re: Zero Unnecessary Temporary Objects: A Revolution

From: David Abrahams (dave_at_[hidden])
Date: 2002-10-13 22:53:34

"Victor A. Wagner, Jr." <vawjr_at_[hidden]> writes:

> At Sunday 2002/10/13 16:39, you wrote:
> 
> >"Terje Slettebø" <tslettebo_at_[hidden]> wrote in message
> >news:058901c272c8$a261f6b0$60fb5dd5_at_pc...
> > >From: "Yitzhak Sapir" <yitzhaks_at_[hidden]>
> >
> > >On Sun, 13 Oct 2002, [iso-8859-1] Terje Slettebø wrote:
> >
> >
> > >As I understand, the only thing you can safely do with an end() iterator is
> > >to compare it with other iterators.
> >
> >    If operator-- is defined on an iterator, and begin() != end(), then it is
> >also safe to decrement an iterator that is equal to end().
> >reverse_iterators depend on this fact.  This is why rbegin().base() ==
> >end().
> 
> I don't see how that follows.  I agree that rbegin().base() == end(),
> but don't see how that implies that ANY operations on end() are legal.

Well, nothing needs to allow operations on end(), because nothing
forbids it. In general, the rule is: if the standard doesn't forbid
it, it is allowed.

That aside, the implementation of reverse_iterator is clearly spelled
out in the standard:

    [lib.reverse.iter.op++]
    24.4.1.3.5 operator++
    reverse_iterator& operator++();
    1 Effects: --current;

So, Terje's argument holds water.

-- 
           David Abrahams * Boost Consulting
dave_at_[hidden] * http://www.boost-consulting.com