Casting.swift

// Feed into swiftc - && ./main to see Swift 4.1 and Swift 4.2 behave differently
// Swift 4.1 results are different for generic and specialized functions, which is probably incorrect

typealias TestedType = Any

func genericLookup<T>() -> T?
{
    let lookupValue: TestedType? = nil
    if let item = lookupValue as? T
    {
        return item
    }
    return nil
}


func specializedLookup() -> TestedType?
{
    let lookupValue: TestedType? = nil
    if let item = lookupValue as? TestedType
    {
        return item
    }
    return nil
}

func testGeneric()
{
    let optional: Optional<TestedType> = genericLookup()
    if case .none = optional
    {
        print("Generic Optional is .none")
    }
    else
    {
        print("Generic Optional is .some")
    }

    if let item: TestedType = genericLookup() {
        print("Your Optional was bound to a \(String(describing: item)) of type \(type(of: item))")
    } else {
        print("This nil is a nil")
    }
}

func testSpecialized()
{
    let optional: Optional<TestedType> = specializedLookup()
    if case .none = optional
    {
        print("Specialized Optional is .none")
    }
    else
    {
        print("Specialized Optional is .some")
    }
    if let item: TestedType = optional
    {
        print("Your Optional was bound to a \(String(describing: item)) of type \(type(of: item))")
    } else {
        print("This nil is a nil")
    }
}


testGeneric()
testSpecialized()