[swift-evolution] Proposal: A standard library Fraction type

T.J. Usiyan griotspeak at gmail.com
Mon Dec 7 08:36:31 CST 2015

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On Mon, Dec 7, 2015 at 7:41 PM, Stephen Canon via swift-evolution <
swift-evolution at swift.org> wrote:

> Can you guys specify some of the use cases that you have in mind for a
> Rational type?  You mention "alleviating the pain points of floating-point
> math,” but rationals tend to be used *very* differently from floating-point
> types in computation.
> Thanks,
> – Steve
> On Dec 7, 2015, at 5:44 AM, Davide De Franceschi via swift-evolution <
> swift-evolution at swift.org> wrote:
> While I agree that a Rational type, one that would preserve quotient and
> denominator info, would be very nice, I think that it's more fit for a Math
> framework.
> If we're just talking about a type that holds precise decimal info, I
> think making NSDecimal (planned to be renamed as Decimal in the future)
> usable is what we should do.
> On 7 Dec 2015, at 10:28, T.J. Usiyan via swift-evolution <
> swift-evolution at swift.org> wrote:
> I'm all for a stdlib Rational Type. I've written one as well and would be
> glad not to have to include it as a dependency everywhere.
> TJ
> On Mon, Dec 7, 2015 at 1:31 PM, Harlan Haskins via swift-evolution <
> swift-evolution at swift.org> wrote:
>> If Swift 3 is going to focus on re-thinking the Numerics in the system,
>> it might be worth considering adding a Fraction (or Rational) type to the
>> standard library. This, coupled with an arbitrary-precision integer type,
>> would be a great way to handle arbitrary-precision decimal arithmetic, and
>> can alleviate almost all the pain points of floating-point math.
>> There exist now some really nice implementations of Fractions, but the
>> ones I’ve seen haven’t been implemented fully generically.
>> My favorite is this one:
>> https://gist.github.com/JadenGeller/5e80ebf32442acc62e8e
>> I’d love to see some standard library support with rock-solid, fast
>> implementations of all the common algorithms (GCD, LCD, LCM, reduction,
>> etc) and good conformance to the builtin integer protocols. Maybe even
>> FloatLiteralConvertible, too, with some logic for converting rational
>> floats.
>> Thoughts?
>> - Harlan Haskins
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