easy use as/is function at function-chain

Asable.swift

protocol Asable {
    func `as`<T>(_ anyType: T.Type) -> T?
    func `is`<T>(_ anyType: T.Type) -> Bool
}
extension Asable {
    func `as`<T>(_ anyType: T.Type) -> T? {
        return self as? T
    }
    func `is`<T>(_ anyType: T.Type) -> Bool {
        return self is T
    }
}

struct A {
    func testA() -> String { return "this is A"}
}
struct B {}

extension A: Asable {}
extension B: Asable {}

let a = A()
a.as(A.self)?.testA()
a.is(A.self)
a.is(B.self)