[Boost-users] Re: boost::iterator_facade problem with postfix increment proxy

From: Jens Theisen (jens.theisen_at_[hidden])
Date: 2005-03-21 14:24:04

David Abrahams wrote:
>>That is, writing
>>
>>*iter++ = some_value;
>>
>>doesn't really do anything but changing a temporary value in the
>>proxy.
> 
> 
> If that's the case, the iterator_facade is choosing
> postfix_increment_proxy instead of writable_postfix_increment_proxy,
> on the basis of the fact that you haven't given the iterator a proxy
> reference type.  I'm not sure I understand the logic behind it, but
> iterator_facade assumes that if your readable iterator doesn't support
> forward traversal, it must have a proxy reference in order to also be
> writable.  If you have a counterexample, it would be good to see it.

My reference type is a simple reference, I want to implement an lvalue 
iterator (at least in some cases).

I am trying to make a proxy iterator that can be attached to different 
implementations of other iterators and compositions thereof.

The problem with Forward traversal is that I can't really compare to 
iterators at the moment. My equals is defined as true iff both sides are 
empty (past the end of the sequence). :-)

I thought changing this would require passing the comparison 
functionality through to the implementations, what I don't really want 
to do; in part because the implementations can be quite nested, so this 
would be a bit slow for something that I need solely as an 
end-of-sequence test.

To be honest, I don't consider this a real problem anymore. I could 
simply attach a counter to the iterators to do the actual comparison.
So, Forward traversal it is.

Thank you for your assistance.

Best regards, Jens