std.rational?

[MrSmith]

On Monday, 30 September 2013 at 12:14:10 UTC, Joseph Rushton 
Wakeling wrote:
> On 27/09/13 20:20, Walter Bright wrote:
>> On 9/27/2013 6:47 AM, Joseph Rushton Wakeling wrote:
>>> [...]
>>
>> Sounds like we have a new champion! Thanks, Joseph!
>
> I've opened up issue tracking on my fork of std.rational:
> https://github.com/WebDrake/Rational/issues
>
> This includes the greatest-common-factor bug discovered by 
> MrSmith and others that I've identified on detailed 
> consideration of the code.  Some are more "need to check out 
> how this works" rather  than "it's a problem" style issues.
>
> Quite a few issues arise out of the fact that David Simcha 
> obviously wanted the rational type to work effectively with any 
> well-defined integer type of any degree of precision -- from 
> the built-in types to std.bigint.BigInt to any arbitrary 
> user-defined integer types.  (I can imagine that David must 
> have been anticipating that people might want to use GMP, for 
> example, or to hook into languages that inherently support 
> arbitrary-precision arithmetic, like Common Lisp, Haskell or 
> Scheme.)
>
> Most Phobos functions don't have such generic support, so David 
> was forced to roll his own solutions, including some templates 
> (isIntegerLike, CommonInteger) to handle these use-cases.  In 
> one case (his least-common-multiple function) there is in any 
> case no Phobos equivalent that I'm aware of.
>
> It seems to me that the best way to handle these issues in the 
> long term is to ensure that Phobos' existing functions are 
> sufficiently generic to handle what std.rational needs.  
> However, it'd be nice to get a working std.rational in place as 
> soon as possible.
>
> So -- what do people advise I do?  Take what I can out of 
> std.rational and submit Phobos patches, or patch it up as it is 
> and submit std.rational for review, with the review process 
> deciding what stays in and what needs to be farmed out to other 
> parts of Phobos?

Here is my thoughts:
1) instead of gcf use updated std.numeric.gcd. Replace lcm, iAbs, 
floor, ceil, round functions with appropriate analogues from 
phobos.
2) instead of isIntegerLike use similar template from std.traits 
(like isIntegral).
3) replace isAssignable by std.traits.isAssignable or better use 
std.traits.isImplicitlyConvertible. Now i am unable to assign 
integer directly to rational, instead i am forced to use 
rational(integer) method;
4) replace CommonInteger by std.traits.CommonType