Swift

Swift Day 21 面向协议编程 POP (重要)

2020-12-27  本文已影响0人  望穿秋水小作坊

一、对 POP 的基础认知

1. 什么是面向协议编程?会取代面向对象编程吗?
2. 回顾 OOP 的三大特性是什么?并说一下继承的经典使用场合
3. 传统 OOP 面临的问题?以及它们的解决方案? (重要)
image.png
4. 如何解决上述 OOP 无法很好解决的问题?
5. POP 的注意点?(说两点即可)

二、优雅的前缀

1. 优雅前缀版本一:如何给系统类(String)扩展自定义(numberCount)方法?
extension String {
    func numberCount() -> Int {
        self.reduce(0) {("0"..."9").contains($1) ? $0 + 1 : $0}
    }
}

print("122abcde10294".numberCount()) // 输出:8
2. 优雅前缀版本二:不和系统冲突
extension String {
    var mj_numberCount: Int {
        self.reduce(0) {("0"..."9").contains($1) ? $0 + 1 : $0}
    }
}

print("122abcde10294".mj_numberCount) // 输出:8
var str = "122abcde10294"
print(str.mj.numberCount) 
struct MJ {
    var str = ""
    init(_ str: String) {
        self.str = str
    }
    var numberCount: Int {
        str.reduce(0) {("0"..."9").contains($1) ? $0 + 1 : $0}
    }
}
extension String {
    var mj: MJ {
        MJ(self)
    }
}
var str = "122abcde10294"
print(str.mj.numberCount) // 输出:8
3. 优雅前缀版本三:扩展类方法、使用泛型
struct MJ<Base> {
    var base: Base
    init(_ base: Base) {
        self.base = base
    }
}

struct Person {
    var age: Int
    var name: String
}


//给 String 扩展
extension String {
    var mj: MJ<String> {MJ(self)}
    static var mj: MJ<String>.Type {MJ.self}
}
extension MJ where Base == String {
    var numberCount: Int {
        base.reduce(0) {("0"..."9").contains($1) ? $0 + 1 : $0}
    }
    static func sayHello() { print("Hello String: ", Base.self)}
}
//给 Person 扩展
extension Person {
    var mj: MJ<Person> {MJ(self)}
    static var mj: MJ<Person>.Type {MJ.self}
}
extension MJ where Base == Person {
    var numberCount: Int {
        return base.age
    }
    static func sayHello() { print("Hello Person: ", Base.self)}
}

var str = "122abcde10294"
print(str.mj.numberCount)                   // 输出:8
String.mj.sayHello()                        // 输出:Hello String:  String
var person = Person(age: 20, name: "carrot")
print(person.mj.numberCount)                // 输出:20
Person.mj.sayHello()                        // 输出:Hello Person:  Person
4. 优雅前缀版本四: 使用协议(最终版)
// 定义基础类,也是扩展前缀
struct MJ<Base> {
    var base: Base
    init(_ base: Base) {
        self.base = base
    }
}

protocol MJCompatible {}
// 在这里扩充 MJCompatible 的方法实现
extension MJCompatible{
    static var mj: MJ<Self>.Type {
        get {MJ<Self>.self}
        set {} // 加 set 适配 mutating 方法
    }
    var mj: MJ<Self> {
        get {MJ(self)}
        set {}
    }
}

struct Person {
    var age: Int
    var name: String
}


//给 String 扩展
extension String: MJCompatible {}
extension MJ where Base == String {
    var numberCount: Int {
        base.reduce(0) {("0"..."9").contains($1) ? $0 + 1 : $0}
    }
    static func sayHello() { print("Hello String: ", Base.self)}
}
//给 Person 扩展
extension Person: MJCompatible {}
extension MJ where Base == Person {
    var numberCount: Int {
        return base.age
    }
    static func sayHello() { print("Hello Person: ", Base.self)}
    mutating func modifyAge(age: Int) {
        base.age = age
        print("enter modifyAge", age, base.age)
    }
}

var str = "122abcde10294"
print(str.mj.numberCount)                   // 输出:8
String.mj.sayHello()                        // 输出:Hello String:  String
var person = Person(age: 20, name: "carrot")
print(person.mj.numberCount)                // 输出:20
person.mj.modifyAge(age: 10)
// (下面没有输出 10,因为MJ(self)值传递,如果把 Person 从 struct 改成 class,就会输出 10)
print(person.age)                           // 输出:20
Person.mj.sayHello()                        // 输出:Hello Person:  Person
5. 利用协议实现类型判断(了解)
image.png
上一篇 下一篇

猜你喜欢

热点阅读