RE: [boost] Views library in vault

From: Moore, Paul (paul.moore_at_[hidden])
Date: 2000-04-20 05:46:24

From: Dave Abrahams [mailto:abrahams_at_[hidden]]
> 
> on 4/19/00 10:11 AM, Gary Powell at Gary.Powell_at_[hidden] wrote:
> 
> > This library also violates the standard rules about adding things
> > to the namespace std. VTL adds new versions of swap to the std
> > namespace so that callers to std::swap using a view will get our
> > version and not the std version. It's the best of a lot of worse
> > choices.
> > 
> > In addition, it violates the rules about forward declarations of
> > container classes. (They are prohibited) These declarations are all
> > in one file, stl_traits.h, so if your compiler has problems 
> > with them you can either include the correct files or fix it. The
> > reasoning is that by forward declaring the containers we can
> > reduce the compile time by elimination of unnecessary parsing.
> > All we are interested in is some trait information about the containers.
> 
> I don't find these to be worth inducing undefined behavior 
> for, and I would avoid using this library for that reason. I
> doubt such a library will find much acceptance in this forum.

On adding stuff to std::, isn't this currently very much a live issue for
debate? As Gary says "it's the best of a lot of worse choices" - I didn't
read this as being a gratuitous violation of the standard, but more a
compromise until the current issues on how to properly extend things like
std::swap for user-defined containers and template stuff is resolved.

On the forward declaration issues, just include the full headers - it's just
a compile time optimisation.

Personally, I have no problem with accepting this for boost, on the basis
that (a) the forward declarations go (maybe leave them as a compile-time
option for people who want to trade safety for compile speed, but definitely
off by default), and (b) there is a clear intention to do "the right thing"
with regard to swap() once it is clear what that is (that may need a
detailed discussion of what the issue is, and why the other choices were
worse).

Paul.