[boost] ctassert again

From: Csaba Szepesvari (szepes_at_[hidden])
Date: 1999-12-09 02:53:10

Oops, sorry, I forgot to include the code.
So please find it attached now. Comments are welcome.
- Csaba

Csaba Szepesvari wrote:

> Dear All,
>
> Attached is the ctassert solution I am using in my projects; it is slightly
> different from the codes that appeared here.
>
> Motivation (see also the documentation):
>
> (R1) A minimal requirement of a good compile time assertion facility is to give
> an error message *at the line* where the assertion fails.
> (R2) Another requirement is that the facility should be usable in both
> declarations and implementations in the same way.
> (R3) The last requirement is that no real code should be generated and no
> storage should be used.
> (R4) No macros.
> (R5) The namespaces should be polluted in a minimal way.
>
> All the above requirements  :-)
> -- except --
> the last two are supported by this implementation :-(
>
> Unfortunately, in order to ensure R1 you need macros. In order to support R2 and
> R3 you need class declarations. Unfortunately, this means some pollution of the
> active scope. It also follows that the macro needs two parameters: the first
> being the constant boolean expression to be evaluated and the second being the
> "name of the check". These names should be different in the same scope for
> repeated usage of this macro - in this respect the code could be improved
> somewhat e.g. using  __line__, etc.
>
> Comments are appreciated.
>
> - Csaba
>
> Dave Abrahams wrote:
>
> > Beman wrote:
> > > One problem we ran into was that we wanted something which was not
> > > subject to inadvertent misuse.  For example, we had several
> > > implementations of a "require" template class, which you could
> > > inherit or instantiate:
> > >
> > >    template<typename T>
> > >    class foo : require< std::numeric_limits<T>::is_integer > {...};
> > >
> > > The problem was that it could be misused:
> > >
> > >    template<typename T>
> > >    class foo
> > >    {
> > >        require< std::numeric_limits<T>::is_integer >;
> > >    };
> > >
> > > This code looks right, but is actually totally ineffective (because
> > > it should have been coded "require<
> > > std::numeric_limits<T>::is_integer > some_name;").
> > >
> > > Any compile time assert should be bullet-proof, IMO.
> >
> > I'm not convinced:
> > 1. compile-time assertions will be primarily for the advanced user and
> > library programmer. The library's clients will get the benefit of the assert
> > at compile time, when used properly
> >
> > 2. The problem you describe is no worse than many other pitfalls in the
> > language; you have to know the language rules.
> >
> > e.g.
> >
> > class mutex;
> > void foo()
> > {
> >     mutex();    // Oops; does nothing!
> >
> >     ...
> > }
> >
> > 3. You could improve things by changing the name to require_t, making the
> > error you describe less likely.
> >
> > -D
> >
> > ------------------------------------------------------------------------
> > eGroups.com Home: http://www.egroups.com/group/boost/
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>
> --
> =======================
> Csaba Szepesvari
>
> Head of Research Department, Mindmaker Ltd., Budapest 1121, HUNGARY
> Konkoly Th. M. u. 29-33
>
> WWW: http://victoria.mindmaker.hu/~szepes
> e-mail: szepes_at_[hidden]
> Tel: [phone]
> Fax: [phone]
>
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--
=======================
Csaba Szepesvari
Head of Research Department, Mindmaker Ltd., Budapest 1121, HUNGARY
Konkoly Th. M. u. 29-33
WWW: http://victoria.mindmaker.hu/~szepes
e-mail: szepes_at_[hidden]
Tel: [phone]
Fax: [phone]