[boost] Re: filter_iterator not bidirectional ?

From: David Abrahams (dave_at_[hidden])
Date: 2003-05-07 11:19:05

Thomas Witt <witt_at_[hidden]> writes:

>> I need it.  I have independently implemented a version of it in CGAL
>> quite some time ago, and I'm comparing it to Boost's version now.
>> Mine has to be bidirectional, so I store the "begin" base iterator.
>> But I was wondering if I could do without, because the only reason
>> for storing
>> the begin base iterator is just to detect when the user calls operator-- on the
>> begin() of the resulting filter iterator.
>> But is this something which really has to be guarded against, or is this just
>> something which can be left unspecified (i.e. it's a user bug) ?
>> 
>
> I tend to agree. Decrementing the begin iterator is never save nor are
> there any guards in the standard library.

If someone would like to contribute a patch and tests that prove it
works, that would be great.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com