Misc Swift

misc.swift

protocol Homogenous {
    func foo(_: Self)
}

extension Homogenous {
    func foo(_: Self) { }
}

extension Int: Homogenous { }

let a: Int = 1
let b: String = "one"

/* Generally, we can't type check using 'is' against a homogenous protocol, 
   but if the variable we are type checking is an optional, we can.
   Why is this?                                       */
let bar: Int? = a
bar is Homogenous         // true
Optional(a) is Homogenous // true

let baz: String? = b
baz is Homogenous         // false

/* generally: 
   error: protocol 'Homogenous' can only be used as a generic constraint 
   because it has Self or associated type requirements */
//a is Homogenous
//b is Homogenous

/* Can we emulate it with a simple 
   enum wrapper of our own? Nope.   */
enum Wrapper<T> {
    case Some(T)
    case None
}

let foo = Wrapper.Some(a)
//foo is Homogenous 
    /* error: protocol 'Homogenous' can only ... */