[swift-evolution] Static Subscript

[Félix Cloutier]

I don't like that the subscript essentially becomes a second call syntax. Can we solve these problems in a different way?

Félix

> Le 28 janv. 2016 à 22:20:01, Dave via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> What do we think about allowing types to have static subscripts?
> struct Foo {
>     static subscript(bar: Bar) -> FooBar {...}
> }
> 
> It could be used to implement umbrella class “initializers” that return subclasses (or anything, really) without relying on Objective-C tomfoolery, since it’s just another function and can return anything you want:
> class Int8Class    : SwiftInteger {…}
> class Int16Class   : SwiftInteger { var x: Int16;  override init() { self.x = 0 }; init(_ x: Int16)  { self.x = x } }
> class Int32Class   : SwiftInteger {…}
> class IntClass     : SwiftInteger {…}
> class BigIntClass  : SwiftInteger {…}
> class SwiftInteger {
>     static subscript()          -> SwiftInteger {…}
>     static subscript(x: Int8)   -> SwiftInteger {…}
>     static subscript(x: Int16)  -> SwiftInteger {…}
>     static subscript(x: Int32)  -> SwiftInteger {…}
>     static subscript(x: Int)    -> SwiftInteger {
>         switch x {
>         case Int( Int8.min)...Int( Int8.max): return Int8Class(Int8(x))
>         case Int(Int16.min)...Int(Int16.max): return Int16Class(Int16(x))
>         case Int(Int32.min)...Int(Int32.max): return Int32Class(Int32(x))
>         default:                              return IntClass(x)
>         }
>     }
> }
> let foo = SwiftInteger[256] //foo is a Int16Class
> 
> Or for creating “functions” that have properties:
> struct add {
>     static let name: String = "add"
>     static var logging = false
>     static private (set) var callCount = 0
>     static subscript(arg1: Int, arg2: Int) -> Int {
>         defer {
>             if add.logging == true {
>                 print("callcount = \(add.callCount): \(add.name)(\(arg1), \(arg2)) -> \(ret)")
>             }
>         }
>         add.callCount += 1
>         let ret = arg1 + arg2
>         return ret
>     }
> }
> let nine = add[4, 5]
> add.logging = true
> let ten = add[4, 6]     // prints “call count = 2: add(4, 6) -> 10"
> 
> Thoughts?
> 
> - Dave Sweeris
> 
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