Boost logo

Boost :

Subject: Re: [boost] [Review] Boost.Ratio
From: joel falcou (joel.falcou_at_[hidden])
Date: 2010-10-09 02:16:56

On 09/10/10 00:16, vicente.botet wrote:
> The idea is to specialize mpl arithmetic operation for ratio. As Ratio is not a Integral Constants we need to define a new on, let me call it Rational Constant. What could be the requirements for a Rational Constant?
> Expression Type Complexity
> r::tag rational_c_tag Constant time.
> r::value_type A boost::rational<integral_type> type Constant time.
> r::num An integral constant expression Constant time.
> r::den An integral constant expression Constant time.
> r::type Rational Constant Constant time.
> r::value_type c = r.value() R::value_type Constant time.
> Expression Semantics
> r::tag r's tag type; n::tag::value is n's conversion rank.
> r::num The value of the numerator integral constant.
> r::den The value of the denominator integral constant.
> r::type 'is_equivalent'<r::type,r>::value == true.
> c=r.value() c.numerator() * r::den == c.denominator() * r::num.
> I could implemented this, but before doing it I will want to heard the maintainers of MPL about this feature and if they will accept to include it in his library.
Oh the idea was not to include ratio in MPL but just make ratio expose
the needed inner type so you could drop any ratio type into mpl operations.
> Respect to fusion adaptors, I don't see what can be done. Could detal a little bit more:

Basically, soemtime I needed to acces the numerator or denominator
through fusion::at_c or apply fusion::for_each on them.

int n = fusion::at_c<0>( some_ratio );

I can make the adaptor if you want, it's like 20 lines. It can sit in an
optional file (much like ratio_io) and be included only if needed.

> I will be glad to see how you applied ratio. Could you share?
Sure, I'll post this once I go back to my office.

Boost list run by bdawes at, gregod at, cpdaniel at, john at