Re: [boost] Re: Re: possible addition to operators library

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2003-03-12 12:01:51

Sam Partington wrote:
> 
> No, I agree.  You're right, much better to squint at error messages than to
> try and diagnose unexpected behaviour.  Plus the messages I compared against
> were not all that bad to look at anyway, and all of them said something to
> the effect of "can't convert class 'A' to 'int' or something.

Fine.

> > The VC issue bothers me, as I don't think I fully understand what
> > exactly happens. Doesn't the compiler give any additional messages to
> > explain
> > what exactly is ambiguous for operator&&? Does anyone know this
> > problem
> > and has a work-around?
> Unfortunately I don't understand this.   It can go in the documentation,
> with the work around to be :
> if (!!a && ...)
> or
>  if (a)
>     if (...)

Of course. But I was hoping for a work-around at the library-side, not
at the user's side. What exactly are the overloads that the VC thinks
might match? Or what type does it try to cast the expression to (instead
of bool)?

> Finally, if we choose this route, this means that we can take the approach
> of providing operator! and a private operator some_number_type() while the
> user provides operator bool.  This is more semantically correct in my
> opinion, anyone have any problems with this?
> 
> Oh, I should have patches posted very soon.

Fine. Remember that the name should probably change to reflect the
"corrected" semantics. Something like 'bool_negatable'?

But then, there is still some slight illogic here: We provide operator!,
but the protector is for operator bool. Two orthogonal concepts. Would
it make sense to separate them? If so, will 'bool_protector' have any
value? Those people not aware of the problem of providing operator
bool() will not use it, those that are aware will use Peter's
safe-bool-idiom when appropriate as it gives better error messages. And
where safe-bool is not applicable, you don't need a protector anyway
AFAICS. Hm... thoughts?

Regards, Daniel

-- 
Daniel Frey
aixigo AG - financial training, research and technology
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