[boost] Re: Library proposal --- pair (and tuple) iterators

From: Anthony Williams (anthony.williamsNOSPAM_at_[hidden])
Date: 2003-09-23 03:32:55

Thomas Becker <tmbecker1_at_[hidden]> writes:
> --- Anthony Williams
>> *it MUST be a real reference to the value type for
>> Forward/bidi/random access
>> Iterators (see table 74 of the standard).
>> 
>
> The zip iterator that's in the Boost CVS right now was
> written under the assumption that the new iterator
> categories are available. These new categories were
> designed primarily to solve the exact (annoying) issue
> with the old categories that you mention: in order to
> have certain traversal properties, such as random
> access, one had to have certain access properties,
> such as *it being a reference. Under the new
> categories, that problem has gone away. Therefore,
> what you have should be very useful in a context where
> only the old categories are available, but is probably
> unneccessarily heavy when the new categories are
> present.

Possibly, but the new categories aren't here yet, are they? They're not even
in the library TR, so code written today still needs to deal with the reality
of the current iterator categoriess. As it stands, the zip iterator can't even
claim to be a forward iterator if it doesn't return a reference from *it,
which makes it useless with a very large category of algorithms, even though it
might otherwise meet all the requirements of a random access iterator.

If you think that this is an acceptable scenario, then that's your choice, and
I'll pursue my submission as an alternative that works with current
algorithms, but is more heavyweight. Otherwise, I'm happy to help enhance zip
iterator to work with the current categories, if you wish.

Anthony
-- 
Anthony Williams
Senior Software Engineer, Beran Instruments Ltd.
Remove NOSPAM when replying, for timely response.