面向协议编程Protocol Oriented Programming简称POP.是Swift的一种编程范式.同时Swift也是一门面向对象的编程语言Object Oriented Programming简称OOP.在Swift中OOP和POP是相辅相成的.POP能弥补OOP一些设计上的不足.

POP的注意点

• 优先考虑创建协议,而不是父类基类
• 优先考虑值类型struct enum,而不是引用类型class
• 巧用协议的扩展功能
• 不要为了面向协议而使用协议

利用协议实现前缀效果

import UIKit
struct LDWrapper<Base> {
    let base: Base
    init(_ base: Base) {
        self.base = base
    }
}
protocol LDCompatible {}

extension LDCompatible {
    static var ld: LDWrapper<Self>.Type {
        get { LDWrapper<Self>.self }
        set { }
    }
    
    var ld: LDWrapper<Self> {
        get { LDWrapper(self) }
        set {}
    }
    
}

extension String: LDCompatible {}

extension LDWrapper where Base == String {
    func numberCount() -> Int {
        var count = 0
        
        for c in base where ("0" ... "9").contains(c) {
            count += 1
        }
        return count
    }
}

var string = "123fds434"
print(string.ld.numberCount())

Base: 类

import UIKit

struct LDWrapper<Base> {
    let base: Base
    init(_ base: Base) {
        self.base = base
    }
}
protocol LDCompatible {}

extension LDCompatible {
    static var ld: LDWrapper<Self>.Type {
        get { LDWrapper<Self>.self }
        set { }
    }

    var ld: LDWrapper<Self> {
        get { LDWrapper(self) }
        set {}
    }

}

extension String: LDCompatible {}

extension LDWrapper where Base == String {
    func numberCount() -> Int {
        var count = 0

        for c in base where ("0" ... "9").contains(c) {
            count += 1
        }
        return count
    }
}

class Person { }
class Student: Person { }
extension Person: LDCompatible { }
extension LDWrapper where Base: Person {
    func run() { }
    static func test() { }
}


Person.ld.test()
Student.ld.test()
let p = Person()
p.ld.run()

let s = Student()
s.ld.run()

Base: 协议

import UIKit

struct LDWrapper<Base> {
    let base: Base
    init(_ base: Base) {
        self.base = base
    }
}
protocol LDCompatible {}

extension LDCompatible {
    static var ld: LDWrapper<Self>.Type {
        get { LDWrapper<Self>.self }
        set { }
    }

    var ld: LDWrapper<Self> {
        get { LDWrapper(self) }
        set {}
    }

}

extension String: LDCompatible {}

extension LDWrapper where Base == String {
    func numberCount() -> Int {
        var count = 0

        for c in base where ("0" ... "9").contains(c) {
            count += 1
        }
        return count
    }
}

class Person { }
class Student: Person { }
extension Person: LDCompatible { }
extension LDWrapper where Base: Person {
    func run() { }
    static func test() { }
}


var s1: String = "123fds434"
var s2: NSString = "123fds434"
var s3: NSMutableString = "123fds434"
print(s1.ld.numberCount())
print(s2.ld.numberCount())
print(s3.ld.numberCount())

extension String: LDCompatible {}
extension NSString: LDCompatible {}
extension LDWrapper where Base: ExpressibleByStringLiteral {
    func numberCount() -> Int {
        let string = base as! String
        var count = 0
        for c in string where ("0" ... "9").contains(c) {
            count += 1
        }
        
        return count
    }
}

利用协议实现类型判断

func isArray(_ value: Any) -> Bool {
    value is [Any]
}
class HomeViewController: UIViewController {
   
    override func viewDidLoad() {
       super.viewDidLoad()
        print(isArray([1,2]))
        print(isArray(["1",2]))
        print(isArray(NSArray()))
        print(isArray(NSMutableArray()))

    }
}

protocol ArrayType { }
extension Array: ArrayType {}
extension NSArray: ArrayType {}
func isArrayType(_ type: Any.Type) -> Bool {
    type is ArrayType.Type
}


class HomeViewController: UIViewController {
   
    override func viewDidLoad() {
       super.viewDidLoad()
        //true
        print(isArrayType([Int].self))
        print(isArrayType([Any].self))
        print(isArrayType(NSArray.self))
        print(isArrayType(NSMutableArray.self))

    }
}