type.swift

protocol Wrapper {
    associatedtype Value
    var value: Value { get set }
    init(value: Value)
    init(_ value: Value)
    func unwrap() -> Value
}

extension Wrapper {
    init(_ value: Value) {
        self.init(value: value)
    }

    func unwrap() -> Value {
        return self.value
    }
}


// doesn't work
/*
extension Wrapper.Value {
    init(_ wrapped: Wrapper) {
        self = wrapped.value
    }
}
*/


// works, but is clunky
protocol WrappedValue {
    associatedtype Parent: Wrapper
    init(_ wrapper: Parent)
}

extension WrappedValue where Parent.Value == Self {
    init(_ wrapper: Parent) {
        self = wrapper.value
    }
}


// Tests
struct IntWrapper: Wrapper {
    var value: Int = 0
}

extension Int: WrappedValue {
    typealias Parent = IntWrapper
}

let one = IntWrapper(1)
print(one.unwrap())
print(Int(one))