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

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2002-10-17 19:31:51

On Thursday, October 17, 2002, at 07:28  PM, Victor A. Wagner, Jr. 
wrote:

> I'm dismayed (slightly) to discover that the containerators I wrote a 
> year ago aren't really conforming bidirectional iterators.  You know, 
> in all that time, nobody's complained?  Am I going to fix them?  Not 
> for the original users,  I don't work there anymore.  Do I think that 
> doubling the memory requirements just so someone can do the equivalent 
> of --end() is worth it?  Not really.  Maybe we need a new class called 
>  either-directional which becomes testable when it "steps off the end" 
> but that can't "come back".

Go for it:

struct eitherdirectional_iterator_tag : std::forward_iterator_tag {};

Now your code can test on the iterator_category being 
eitherdirectional_iterator_tag, and act accordingly.  And when you send 
your iterator to code ignorant of your new classification (such as 
std::algorithms) it will still function well as a forward iterator 
(provided you've met those constraints).

-Howard