Re: c++ "with" keyword

[Gianni Mariani <gmariani at chaincast dot com>]

Andrew Haley wrote:

> Momchil Velikov writes:
> > >>>>> "Robert" == Robert Dewar <dewar@gnat.com> writes:
> > 
> >     Robert> If you think "with" is valuable, then the task is to
> >     Robert> convince the guardians of the C++ standard of this. If
> >     Robert> you can't convince the
> > 
> > Not related to this particular "with" discussion, but I couldn't
> > disagree more.  A standards body should not invent language
> > "features", but rather codify existing (proven) extensions.
>
> I totally agree.  A standards should not invent language features, or
> -- heaven forbid -- programming languages.  The reason for this is
> pretty obvious, in that once a feature is standardized it's too late
> to remove it if it has some fatal flaw.
>  
I agree as well.

Proposals of language extensions should come from anyone :)  The metrits 
discussed in community and accepted as a standard once it is generally 
accepted.

So, I'd like to steer the discussion back to the merits of "with".

The "with" syntax was a pain in the rear in Pascal and I never want to 
see it again - this is why:

Take 2 structures, A and B which are both used in a "with" statement.

e.g. (I'll use the proposed new "with" syntax in c++ below)

Let's start with some valid working code ...

struct A {
   int    X;
   int    Y;
   int    hUgH;
};

struct B {
   int    Z;
};

int func()
{
       ....
       A & a;
       B & b;
       ....

       with ( a )
       witb ( b )
       {

           Y = Z;
           hUgH = X; //  woz this then eh ? <-- point of confusion
       }
       ...
}

And a little later someone comes and fixes a bug and adds

struct B {
   int    Z;
   int    X;    // need an X to fix The Bug (tm)
};

Oops - which X is now instantiated at "point of confusion" ?

Someone innocently added a new member and completly changed the 
behaviour of the code.  For code maintainability, I'd suggest that this 
would cause more difficult to discover problems than would be merited.

This is also one of the reasons I don't like namespaces much either - 
hence I allways prefix identifiers that are not within a class's scope.

If you were to implement (heaven forbid) the "with" mechanism, I'd 
suggest you use the "using" keyword instead.

G