Re: [boost] [review][constrained_value] Review ofConstrainedValueLibrary begins today

Subject: Re: [boost] [review][constrained_value] Review ofConstrainedValueLibrary begins today
From: Robert Kawulak (robert.kawulak_at_[hidden])
Date: 2008-12-05 22:31:52

> From: vicente.botet

> >> I would prefer 
> >> to have two separated hierarchies, one for constrained values 
> >> that preserv its constraints, error handling, ... staticaly, 
> >> and one for those tyhe constraint can be changed at runtime.
> > 
> > I wouldn't prefer to have two separate hierarchies with 
> almost identical
> > functionality and differing only in details.
> 
> Well we can have a single type that cover with the whole 
> domain, but we will need more metaprogramming.

We already have a single type that covers both static and dynamic constraints,
so what is the point? Did I misunderstood something?

> I expect that a constrained integer will have the same size 
> as an int, i.e. sizeof(int). Which is the size of an instance 
> of the constrained class?

Here are some examples:

GCC 4.3.2:

        4 = sizeof (int)
        4 = sizeof (bounded_int<int, 0, 128>::type)
        12 = sizeof (bounded<int, int, int>::type)
        4 = sizeof (constrained<int, is_even>)

MSVC 8.0 SP1:

        4 = sizeof (int)
        8 = sizeof (bounded_int<int, 0, 128>::type)
        20 = sizeof (bounded<int, int, int>::type)
        8 = sizeof (constrained<int, is_even>)

I don't know why MSVC cannot opimise the size as well as GCC, but anyway the
library allows for perfect size optimisation with some compilers.

> See below one possible implementation of static_constrained. 
> Of course, the implementation is not complete.
[snip]
> typedef static_constrained<even_traits> even_type;
> 
> int main() {
>     even_type a(2);
>     std::cout << "sizeof(even_type)=" << sizeof(even_type) << 
> std::endl;
>     even_type b(1);  // throws
> }

So how is this different from:

        typedef constrained<int, is_even> even_type;

?

Best regards,
Robert