Re: [boost] (infinite) sequences using recurrence relations

From: John E. Potter (jpotter_at_[hidden])
Date: 2001-08-10 23:11:28

On Fri, 10 Aug 2001, Douglas Gregor wrote:

> The code posted is more along the lines of an iterator adaptor. Consider the 
> transform_iterator_adaptor from the iterator adaptors library, but with a 
> function object that has side effects. operator* must be stable, so we have 
> to cache the value. The some_input_iterator code posted is a skeletal 
> description of how one would make transform_iterator_adaptor conform to the 
> input iterator concept regardless of any side effects due to calling the 
> function.

Sorry, I missed the whole point because of the attempt to provide some
unrequired meaning for operator==.  The shared cache is not required.
The point that I could not see is that operator* returns the cache
and operator++ calls the function.  Implementing an input_iterator is
not difficult, but it may be made difficult. :)

> I think we all agree on stable operator*.

I think that is a dangerous assumption.  There may even be an open
issue in the LWG.

I have refined my views on operator==.  Thanks for the discussion.
The problems are realy not important because for input_iterators,
"In the end there can only be one". <g>

John