compilercrashesdemo.swift

//------------------------------------------------------------------------------
// The following compiles and works, but see comments for 2 compiler crashers.
//------------------------------------------------------------------------------
protocol DefaultInitializable { init() }
extension Int: DefaultInitializable {}
// Hople = Homogeneous tuple / static array implemented using recursive structs.
protocol HopleType : DefaultInitializable {
    typealias Element: DefaultInitializable
    subscript(index: Int) -> Element { get set }
}
struct EmptyHople<Element : DefaultInitializable> : HopleType {
    init() {}
    subscript(i: Int) -> Element { // <--- Replacing i with _ crashes compiler.
        get { fatalError("Index out of bounds!") }
        set { fatalError("Index out of bounds!") }
    }
}
struct HopleAfter<Tail : HopleType> : HopleType {
    var head: Tail.Element
    var tail: Tail
    init() { (head, tail) = (Tail.Element(), Tail()) }
    subscript(i: Int) -> Tail.Element {
        get { if i == 0 { return head } else { return tail[i - 1] } }
        set { if i == 0 { head = newValue } else { tail[i - 1] = newValue } }
    }
}
struct HopleOf<Element: DefaultInitializable> {
    typealias Count0 = EmptyHople<Element>
    typealias Count1 = HopleAfter<Count0>
    typealias Count2 = HopleAfter<Count1>
    typealias Count3 = HopleAfter<Count2>
}
var a = HopleOf<Int>.Count3() // <--- Replacing var with let crashes compiler.
a[0] = 1
a[1] = 2
a[2] = 3
print(strideofValue(a)) // 24 (ie stride of three Ints, 3 * 8)
print(a[0]) // 1
print(a[1]) // 2
print(a[2]) // 3