Re: [Boost-users] [units][interval] adapt boost.interval for boost.units

24 May 2010

      On May 23, 10:12 pm, alfC <alfredo.cor...@gmail.com> wrote:
...
boost::numeric::interval<boost::units::quantity<boost::units::si::energy>
   iv(3.*boost::units::si::meter, 4.*boost::units::si::meter);
doesn't compile because of an error in boost/numeric/interval/
checking.hpp (error attached below).
answering to myself... I hope this is useful for someone and for the
Units and Interval maintainers.

Boost Interval has an unfortunate line of code in boost/numeric/
interval/checking.hpp that reads

	static T empty_lower()
	{
		return (std::numeric_limits<T>::has_quiet_NaN ?
					std::numeric_limits<T>::quiet_NaN() : static_cast<T>(1) // units
can not be constructed from plain numbers (int or other)
		);
	}
inside the template class 'checking_base'. The trick to make interval
work with units is to specialize the class checking_base to change the
behaviour of this particular function.
Also unfortunate is the fact that the checking_base member functions
are defined inside the class so the whole checking_base class has to
be rewritten during the specialization, including member functions
that remain unchanged. So if you want to declare a units interval as

boost::numeric::interval<boost::units::quantity<boost::units::si::energy>
...
you need to include the code below

(see at end).

The code seems to be as generic as possible, it should work with any
unit.

Now I still have two questions: Whether it is possible to add a
shorter specialization code that only specializes only empty_lower().
The second question is what is the magic that makes units
constructible from integer 0 and not from integer 1 (note that because
of this I can keep empty_upper unchanged).

Thank you,
Alfredo

adaptation of Boost.Interval for Boost.Units:

namespace boost {namespace numeric {namespace interval_lib {
template<class Unit>
struct checking_base<boost::units::quantity<Unit> >{
	typedef boost::units::quantity<Unit> T;   //this is to keep most of
the code unchanged
	static T pos_inf(){
		assert(std::numeric_limits<T>::has_infinity);
		return std::numeric_limits<T>::infinity();
	}
	static T neg_inf(){
		assert(std::numeric_limits<T>::has_infinity);
		return -std::numeric_limits<T>::infinity();
	}
	static T nan(){
		assert(std::numeric_limits<T>::has_quiet_NaN);
		return std::numeric_limits<T>::quiet_NaN();
	}
	static bool is_nan(const T& x){
		return std::numeric_limits<T>::has_quiet_NaN && (x != x);
	}
	static T empty_lower(){
		return (std::numeric_limits<T>::has_quiet_NaN ?
			std::numeric_limits<T>::quiet_NaN() : T::from_value(1)      // <--
basically the only change
		);
	}
	static T empty_upper(){
		return (std::numeric_limits<T>::has_quiet_NaN ?
					std::numeric_limits<T>::quiet_NaN() : static_cast<T>(0)
		);
	}
	static bool is_empty(const T& l, const T& u){
		return !(l <= u); // safety for partial orders
	}
};
}}}