Re: [Boost-users] [mpl, units] rational and static_rational

[Matthias Schabel]

> I am looking for a template library that can handle compile time
> rationals, ideally with a similar interface to mpl::int_ and that
> plays well with boost::rational (the dynamic type).
>
> First I found boost/mpl/math/rational_c.hpp but soon I realized that
> it doesn't work with basic operations like mpl::plus, it doesn't even
> simplify reducible fractions (i.e. 2/4 -> 1/2), in fact it looks like
> it is just the storage of two (static) integers. Is this something
> that will be developed in the future or am I using it in the wrong
> way?
>
> Then I found boost::units::static_rational which is more promising,
> because it simplifies fractions and works with mpl::plus, but it is
> not integrated with boost::rational nor has an interface similar to
> that of mpl metatypes.
>
> Is there a way of extending mpl::math::rational_c with the existing
> libraries in boost, or a simple way to make
> boost::units::static_rational have an interface similar to mpl and
> also have a value type that returns it runtime boost::rational value?

I certainly would have no objection to repackaging the static_rational
type used in Boost.Units as an MPL type that plays nicely with
Boost.Rational. My advice would be to put together a functional
implementation and propose it for a mini-review. We could easily
typedef units::static_rational -> mpl::rational_ in the units library.

Matthias
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[Steven Watanabe]

AMDG

Matthias Schabel wrote:
>> I am looking for a template library that can handle compile time
>> rationals, ideally with a similar interface to mpl::int_ and that
>> plays well with boost::rational (the dynamic type).
>>
>> First I found boost/mpl/math/rational_c.hpp but soon I realized that
>> it doesn't work with basic operations like mpl::plus, it doesn't even
>> simplify reducible fractions (i.e. 2/4 -> 1/2), in fact it looks like
>> it is just the storage of two (static) integers. Is this something
>> that will be developed in the future or am I using it in the wrong
>> way?
>>
>> Then I found boost::units::static_rational which is more promising,
>> because it simplifies fractions and works with mpl::plus, but it is
>> not integrated with boost::rational nor has an interface similar to
>> that of mpl metatypes.
>>
>> Is there a way of extending mpl::math::rational_c with the existing
>> libraries in boost, or a simple way to make
>> boost::units::static_rational have an interface similar to mpl and
>> also have a value type that returns it runtime boost::rational value?
>
> I certainly would have no objection to repackaging the static_rational
> type used in Boost.Units as an MPL type that plays nicely with
> Boost.Rational.

The main issue will be that Boost.Units requires unique types
(to keep template instantiations down). MPL doesn't care about
unique types.

> My advice would be to put together a functional implementation and
> propose it for a mini-review. We could easily typedef
> units::static_rational -> mpl::rational_ in the units library.

You can't typedef a template like that.

In Christ,
Steven Watanabe