Re: [boost] [mpl::math Rational] type member

From: Andy Little (andy_at_[hidden])
Date: 2005-10-24 10:32:49

>>>> "David Abrahams"  wrote
>>>>> "Andy Little" writes:
>>>>
>>>>> I don't see what the presence of numerator and denominator has to do
>>>>> with normalization.
>>>>
>>>> They should be typedefs for  the input parameters?
>
> Hmm, is that meant to be a question?

As it stands in both my and Cromwells version the numerator and denominator are
those of the (so-called) normalized version. This was carried over from the
runtime version by Matthias Schabel in his original compile-time rational. IOW
to the compile time rational veterans thats how its always been and we thought
it worked fine. The rationale is that rational is primarily a math entity,
whereas integral can be used as an id and for counting, iterating etc.  So the
question is do you think they should rather be typedefs for  the input
parameters?

>>> What does that have to do with normalization?
>>
>> Are you referring to my use of the word 'normalisation'
>
> Yes.
>
>> to mean  making
>> my_rational<2,8>::type == my_rational<1,4>? Maybe the use of  the word
>> normalisation here is not correct. Is that the problem?
>
> No.  Please take me literally.  I don't see any relationship between
> whether we provide numerator/denominator member typedefs and
> normalisation (or normalization).

As it stands these two typedefs are normalized versions of the Numerator and
Denominator parameters.

[cut]

>> Its difficult to know what you mean.
>> Do you mean something like:
>>
>> template <
>>     typename  Numerator,
>>     typename Denominator
>>>
>> where Denominator == One
>> struct my_rational : Numerator {/*...*/};
>
> Yes, something like that.  Maybe a silly idea, but not insane.

I experimented with the integral / rational relationship. My view is that it is
unwise to couple the two together too closely. One example is in division.
divides<int<1>,int<2> > isnt the same as divides<int_<1>, rational<2,1> >, That
can only be enforced if there is no hidden conversion from rational to integral.

regards
Andy Little