Andy Little writes:
The problem: For some Integral Constants values mpl::divides<A.,B> truncates.
Yep. Note that it's no different than int divides( int A, int B ) { return A / B; }
The solution: A new operator... mpl::rational_divides<A,B> When it is desired not to truncate, this form will preserve the fractional part by if necessary converting to a rational number. With this operator in place it is also possible to 'reduce' rationals to integers where possible and further to keep integral constants as integral types by default, knowing that conversion will be automatic if a fraction is required to prevent loss of precision.
Could you provide a specific use case where the above would be preferable over something like mpl::divide< to_rational<A>,B > ?
No mpl::divides<A.,B> is available if A or B is a rational types, because it is assumed that if you are using rationals you require the fraction preserving behaviour.
I'd assume that 'divides' on rational types actually wouldn't truncate anything. Why one would prefer to have a separate metafunction for doing the right thing instead of simply overriding the standard one?
A numeric_cast to an integral type can be used to solve this where necessary.
Errors of using divides<A,B> on rationals will show at compile time.
Thanks to Alexey Gurtovoy for the conversion mechanism
You're welcome! -- Aleksey Gurtovoy MetaCommunications Engineering