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

[James Campbell]

Yes that is the main purpose. At least 2 of the solutions define protocols
which at the very least may be useful to have in the standard library.

On Thu, Jan 7, 2016 at 3:29 PM, Matthew Johnson <matthew at anandabits.com>
wrote:

>
> On Jan 7, 2016, at 9:01 AM, James Campbell via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> 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)
>
>
> Is the goal of looking at approaches that are possible in the existing
> language to identify how the language could be improved to better
> facilitate type safe calculations?  That seems relevant for this list.  But
> if you get too far into collaborating on solutions you want to use today,
> that might be a conversation for the swift-users list.
>
>
> 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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>>
>>
>
>
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> +44 7523 279 698
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>


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