[swift-evolution] [Pitch] Add the sign method to the SignedNumberType protocol.

[David Sweeris]

Sorry, I misspoke. I just meant define it like this:
public enum IntegerSign<T: SignedIntegerType> : Int {
    case Negative = -1
    case Zero = 0
    case Positive = 1
    public var signum: T {
        return T(self.rawValue.toIntMax())
    }
}

Although, come to think of it, I’m not sure if that’s an exact drop-in replacement for your code, since it’s `SignedIntegerType` instead of `SignedNumberType`

-Dave Sweeris

> On May 23, 2016, at 11:48 PM, Charlie Monroe <charlie at charliemonroe.net> wrote:
> 
> Sure, that's a good idea, though I'd personally use the signum var, since using rawValue seems like a bit of an abuse of the fact the enum is defined this way and doesn't help readability of the code:
> 
> enum IntegerSign<NumberType: SignedNumberType>: RawRepresentable {
> 
>     case Negative
>     case Zero
>     case Positive
>     
>     init?(rawValue: NumberType) {
>         if rawValue == -1 {
>             self = .Negative
>         } else if rawValue == 0 {
>             self = .Zero
>         } else if rawValue == 1 {
>             self = .Positive
>         } else {
>             return nil
>         }
>     }
>     
>     var rawValue: NumberType {
>         return self.signum
>     }
>     
>     var signum: NumberType {
>         switch self {
>         case .Negative:
>             return -1 as NumberType
>         case .Zero:
>             return 0 as NumberType
>         case .Positive:
>             return 1 as NumberType
>         }
>     }
>     
> }
> 
> extension SignedNumberType {
>     var sign: IntegerSign<Self> {
>         if self == 0 {
>             return .Zero
>         } else if self > 0 {
>             return .Positive
>         } else {
>             return .Negative
>         }
>     }
> }
> 
> 
> 
>> On May 24, 2016, at 6:09 AM, David Sweeris <davesweeris at mac.com <mailto:davesweeris at mac.com>> wrote:
>> 
>> Can we make it RawRepresentable? That way signum can just return self.rawValue
>> 
>> Sent from my iPhone
>> 
>> On May 23, 2016, at 06:05, Charlie Monroe via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> The clean way would be to make it an enum with var signum that would return -1, 0, 1:
>>> 
>>> enum IntegerSign<NumberType: SignedNumberType> {
>>> 
>>>     case Negative
>>>     case Zero
>>>     case Positive
>>> 	
>>>     var signum: NumberType {
>>>         switch self {
>>>         case .Negative:
>>>             return -1 as NumberType
>>>         case .Zero:
>>>             return 0 as NumberType
>>>         case .Positive:
>>>             return 1 as NumberType
>>>         }
>>>     }
>>> 	
>>> }
>>> 
>>> extension SignedNumberType {
>>>     var sign: IntegerSign<Self> {
>>>         if self == 0 {
>>>             return .Zero
>>>         } else if self > 0 {
>>>             return .Positive
>>>         } else {
>>>             return .Negative
>>>         }
>>>     }
>>> }
>>> 
>>> Charlie
>>> 
>>>> On May 23, 2016, at 9:29 AM, Haravikk via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> 
>>>> Could you give an example of this method’s usage? Surely your value is either positive, negative or zero already, so this method doesn’t return anything more useful.
>>>> 
>>>> In other words, anywhere that I might do this:
>>>> 
>>>> 	if myValue.sign > 0 { … }
>>>> 
>>>> I could just as easily do:
>>>> 
>>>> 	if myValue > 0 { … }
>>>> 
>>>> To the same end result surely? Unless I’m missing something it seems redundant.
>>>> 
>>>> If there is a use-case for this, would it make more sense to have the return type as an enum with cases for Positive, Negative and Zero?
>>>> 
>>>>> On 22 May 2016, at 08:07, Adam Nemecek via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> Howdy,
>>>>> I think that the SignedNumberType should implement a method called sign that will return -1 for negative numbers, 0 for 0 and 1 for positive numbers. This is similar to the signum method in e.g. Java and similarly called methods in other languages.
>>>>> 
>>>>> The implementation is fairly straight forward
>>>>> 
>>>>> extension SignedNumberType {
>>>>>   var sign: Self {
>>>>>     if self == 0 {
>>>>>       return 0
>>>>>     }
>>>>>     else if self > 0 {
>>>>>       return 1
>>>>>     }
>>>>>     return -1
>>>>>   }
>>>>> } 
>>>>> 
>>>>> I was trying to implement is without branching by doing (x > 0) - (x < 0) but I couldn't get the types right so I'm open to suggestions.
>>>>> 
>>>>> 
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>>>> 
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