Re: [boost] Re: Boost Array Initialization Technique

From: christopher diggins (cdiggins_at_[hidden])
Date: 2005-05-31 19:18:38

----- Original Message ----- 
From: "AlisdairM" <alisdair.meredith_at_[hidden]>
To: <boost_at_[hidden]>
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