Convert to chain-invocation

InstantMap.swift

protocol InstantMap {
    func instantMap<T>(_ transform: (Self)->T) -> T
    func instantFlatMap<T>(_ transform: (Self)->T?) -> T?
}

extension InstantMap {
    func instantMap<T>(_ transform: (Self)->T) -> T {
        return transform(self)
    }
    func instantFlatMap<T>(_ transform: (Self)->T?) -> T? {
        return transform(self)
    }
}

extension Int: InstantMap {}
3.instantMap({ $0 + Int(arc4random_uniform(32)) })
3.instantMap({ String($0) })

extension String: InstantMap {}
if true {
    let imageUrlStr: String? = "https://m.baidu.com"
    if let u = imageUrlStr?.instantFlatMap({ URL.init(string: $0) }) {
        print(u)
    }
    if let imageUrlStr = imageUrlStr, let u = URL.init(string: imageUrlStr) {
        print(u)
    }
}