----- Original Message ----- From: "AlisdairM" <alisdair.meredith@uk.renaultf1.com> To: <boost@lists.boost.org> Sent: Tuesday, May 31, 2005 7:52 PM Subject: [boost] Re: Boost Array Initialization Technique
christopher diggins wrote:
This is much more flexible and it allows us to have constructors in boost::array thus making it a full reversible container.
boost::array can never be a standard conforming container because it does not support insertion/removal of elements - it is a fixed size.
I believe the standard only requires insertion/removal of elements on sequences but not containers.
When array was first proposed for TR1 we made suggestions to revise the container concepts to support both 'fixed size' and 'dynamic' containers. The consensus was that this was too much fiddling just to make array into a container. Instead, it was accepted as-is, as a 'container-like' class template.
My points are that an alternative approach which would require less fiddling with the standard would have been to have uninitialized arrays have a size() of zero. Despite being not "array-like" it would help reduce the possibility of bugs. Furthermore as I pointed out in my previous post being "container-like" does more harm than good, because it simply can not be used safely where a container is expected, and leaves the dangerous illusion that it can. As a result, mixed messages will be sent to the programmers. I can just imagine the chaos that is going to erupt on the newsgroups if this gets into the standard as is: Newbie: array causes my existing code base for dealing with containers to break. Guru: array isn't a container Newbie: but it looks just like a container Guru: yes, it is container-like Newbie: what does that mean? Guru: it means that it looks like a container, but it shouldn't be used as a container Newbie: why was that done? Guru: *shrugs*
Aggregate initialization is an important part of the array concept,
I think precisely ust how important is debateable.
allowing it to act largely as a plug-in replacement for language arrays, with the bonus it can be passed by value as well as by reference. The main drawback here is that we cannot deduce the size of a boost::array, as you can with a language array.
Christopher Diggins http://www.cdiggins.com