Re: [Boost-users] Minor refinements for boost::rational

From: Daniel Krügler (dsp_at_[hidden])
Date: 2005-08-23 01:17:14

Daryle Walker wrote:
> Wouldn't that be giving away an implementation detail?  I wonder if we could
> use the gcd & lcm functions I defined in boost::math?  (They were written
> after boost::rational was.)

1) The argumentation should be vice versa: The **current** interface of
the gcd and lcm function templates **is** implementation-driven! The 
reason is that these functions would otherwise need to make a copy of 
their arguments - all but not the second argument of the lcm function.
This is also documented in the code of gcd function template.

This might sound nitty-picky on the first view, but please consider that 
the rational class template is explicitely designed to handle arbitrary
integer-like underlying types, thus including a possible
unlimited-precision integer type (which is currently under proposal for
standard C++) - this is explicitely expressed in

http://www.boost.org/libs/rational/rational.html

Therefore any **unnecessary** argument copies should be prevented. I
proposed boost::call_traits because it was already used in this header 
(in the definition of the rational class template itself).

2) It seems as if the functions of common_factor_rt are prepared for
that, although I only skimmed over the code. Honestly from the current
boost docs in

http://www.boost.org/libs/math/doc/common_factor.html

I could not extract the exact requirements on the template parameter for
common_factor_rt. It just says "This type should be a numeric type that
represents integers". What does that mean under the language 
restrictions of C++?
(Note that the boost::rational docs describe specific requirements on
this type, see corresponding section "Integer Type Requirements")

Greetings,

Daniel