[swift-evolution] Support for newtype feature/typesafe calculations

James Campbell james at supmenow.com
Thu Jan 7 09:01:23 CST 2016

Interesting could you upload :) would be good to consolidate all the
approaches we have right now so we can come up with the best one:

So far we have:

- Box/Unit Type Protocol (My Solution)
- Math Group Protocol (Tino Heth)
- Computed typealias (John Randolph)

On Thu, Jan 7, 2016 at 2:55 PM, John Randolph via swift-evolution <
swift-evolution at swift.org> wrote:

> On Jan 7, 2016, at 4:06 AM, James Campbell via swift-evolution <
> swift-evolution at swift.org> wrote:
> So this is how this feature could be achieved right now with minimal
> changes to the language.
> - We expose some kind of protocol that allows you to Box up types, we
> could call this `Box` or something else like `Unit`. (I have a working
> implementation in the current language with a bit of boilerplate). This
> protocol handles the default implementation of converting from literals and
> to floats etc.
> - For each type-safe unit for a calculation - you define a protocol
> extending this `Box` type which defines the associated type of the value
> that unit holds. For example for Degree and Radian I declared a `AngleType`
> which set the associated type to be a double.
> - For each unit type, you declare a struct that inherits from that
> protocol you defined. So I have two structs `Degree` and `Radian` which
> implement the `AngleType` protocol.
> - You implement the functions for figuring out if your units are equal and
> all other operators they may need i.e `Degree(360) - 30`.
> I took a different approach to this, which was to just typealias Angle to
> Double,  keep all Angle values as radians (since the stdlib trig functions
> take radians), and add some computed setters and getters to let me access
> an Angle in radians, degrees, or grads.
> I would like to see Angle, along with several other basic geometric
> concepts, promoted to the Swift standard library.
> -jcr
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 Wizard
james at supmenow.com
+44 7523 279 698
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