Re: [Aqsis-development] [Aqsis-commits] SF.net SVN: aqsis: [959] trunk/aqsis/aqsistypes/aqsis_types.h

[Chris F. <fo...@ph...>]

On Sat, Apr 21, 2007 at 11:37:26AM -0400, aj...@sp... wrote:
> G'day all.
> 
> Quoting Anteru <An...@sh...>:
> 
> > Yeah, just take by const T&, this does not affect numeric types at all,
> > at least with the compilers I tested it last time.
> 
> If you're concerned, though, there's a Boost recipe for this.
> 
> If you #include <boost/call_traits.hpp>, then:
> 
>     boost::call_traits<T>::param_type is the "best" way to pass a
>     parameter of type T to a function.
> 
> The best way to pass an int is "int const".  The best way to pass a
> CqClass is "CqClass const &".
> 
>     boost::call_traits<T>::value_type is the "best" way to return a
>     value of type T from a function.
> 
> The use of value_type isn't immediately obvious, but the main use is
> for C arrays.  The best way to return int[3] is "const int *".

Thanks Andrew, that's very intersting and informative.

I an implementation, but it seems like the compiler is having trouble
deducing the template parameter types, which kind of defeats the purpose
of the exercise :(.  In particular, I wrote a 'clamp3' in the obvious
way:

template<typename T>                                                                    inline typename boost::call_traits<T>::value_type clamp3(                                           typename boost::call_traits<T>::param_type a,
            typename boost::call_traits<T>::param_type min,                                         typename boost::call_traits<T>::param_type max)
{
    return a < min ? min : (a > max ? max : a);
}

but then to use it I have explicitly specialise:

clamp3<double>(a,min,max)

which isn't very nice at all.  It does however recover the efficency of the
simple pass-by-value version.  Any ideas for a workaround?

~Chris.