The Y Combinator in Swift

Y.swift

public func unsafeCoerce<A, B>(_ x : A) -> B {
    return unsafeBitCast(x, to: B.self)
}

func Y<A>(_ f : @escaping (A) -> A) -> A {
    return { (x : @escaping (A) -> A) in
        return f((x(unsafeCoerce(x))))
    }({ (x : A) -> A in
        let fn : (A) -> A = unsafeCoerce(x)
        return f(fn(x))
    })
}