# Boost :

From: Cromwell Enage (sponage_at_[hidden])
Date: 2005-10-31 15:48:43

--- Andy Little wrote:
> Shouldn't the two parts be described as integer_part
> and fractional_part?

IMHO integer_part is not as descriptive as whole_part.

> And also ... Why do they need to be macros?

The default implementations of whole_part and
rational_part assume that the numeric constant is
already a Mixed Number, with nested whole_part and
rational_part typedefs. Any numeric constant that
wants to be treated as a Mixed Number but can't
provide these typedefs (e.g. double_c) must provide
the necessary metafunction class specializations.
However, for Rational Constants, whole_part and
rational_part can be specialized in terms of the
numerator and denominator metafunctions. If there are
at least two such models of Rational Constants, the
specialization code of whole_part and rational_part
would have to be duplicated for each model. The
macros are there to minimize this duplication. The
same goes for the numerator and denominator of Mixed
Numbers.

[snip concepts discussion, started on new thread]

> Also, Cromwell, do you think that rational numerator
> and denominator should be evaluated eagerly (as it
> currently is) or alternatively lazily, so that it
> would need some function to normalise the rational
> before or maybe during math?

I've exposed simplified_rational for use by those
metafunctions that are guaranteed to return relatively
prime numerators and denominators, e.g.
rational_part_impl<double_tag>::apply. Those numeric
metafunctions that cannot provide this guarantee must
use either rational or rational_::simplify.

> (FWIW my vote is to stay with current behaviour
> though using rational<numerator,denominator> for
> ::type member.)

Is the current definition sufficient?

template <typename N, typename D>
struct rational : rational_::simplify<N,D>::type
{
};

> Meanwhile keep up the good work..

Thanks!
Cromwell D. Enage

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