Swift利用协议实现前缀功能
想要实现的功能
计算字符串中数字的个数
var greeting = "1234-Hello, playground-1234"
extension String {
var numberCount: Int {
var number = 0
for c in self where ("0"..."9").contains(c){
number += 1
}
return number
}
}
print(greeting.numberCount)
存在的问题
直接给一个类增加扩展，容易导致冲突。
解决方案
属性前增加前缀（不优雅）
var greeting = "1234-Hello, playground-1234"
extension String {
var zy_numberCount: Int {
var number = 0
for c in self where ("0"..."9").contains(c){
number += 1
}
return number
}
}
print(greeting.zy_numberCount)
点语法增加前缀
print(greeting.zy.numberCount)
一、持有属性方式
- 结构体ZY持有str，并在构造方法中初始化
- 字符串扩展持有zy计算属性
缺点：
- 不灵活，比如无法给数组扩展功能
var greeting = "1234-Hello, playground-1234"
struct ZY {
var str: String
init(_ str: String) {
self.str = str
}
var numberCount: Int {
var number = 0
for c in str where ("0"..."9").contains(c){
number += 1
}
return number
}
func test() {
print("---test---")
}
}
extension String {
var zy: ZY { ZY(self) }
}
print(greeting.zy.numberCount)
greeting.zy.test()
二、使用范型
缺点：使用繁琐，需要给每一个类扩充功能
var greeting = "1234-Hello, playground-1234"
struct ZY<Base> {
var base: Base
init(_ base: Base) {
self.base = base
}
}
extension String {
var zy: ZY<String> { ZY(self) }
}
class People {}
extension People {
var zy: ZY<People> { ZY(self) }
}
extension ZY where Base == String {
var numberCount: Int {
var number = 0
for c in base where ("0"..."9").contains(c){
number += 1
}
return number
}
func test() {
print("---test---")
}
}
extension ZY where Base: People {
func run() {
print("person run")
}
}
print(greeting.zy.numberCount)
greeting.zy.test()
var person = People()
person.zy.run()
给String扩充类型方法
struct ZY<Base> {
var base: Base
init(_ base: Base) {
self.base = base
}
}
extension String {
var zy: ZY<String> { ZY(self) }
static var zy: ZY<String>.Type { ZY<String>.self }
}
extension ZY where Base == String {
var numberCount: Int {
var number = 0
for c in base where ("0"..."9").contains(c){
number += 1
}
return number
}
func test() {
print("---test---")
}
static func staticTest() {
print("---static test---")
}
}
String.zy.staticTest()
三、利用协议实现前缀
var greeting = "1234-Hello, playground-1234"
/// 前缀类型
struct ZY<Base> {
var base: Base
init(_ base: Base) {
self.base = base
}
}
/// 利用协议扩展前缀属性
protocol ZYCompatible {}
extension ZYCompatible {
var zy: ZY<Self> {
set {} // 使mutating方法编译通过
get { ZY(self) }
}
static var zy: ZY<Self>.Type {
set {} // 使mutating方法编译通过
get { ZY<Self>.self }
}
}
/// 给字符串扩展功能
/// 让 String 拥有 zy 前缀属性
extension String: ZYCompatible {}
/// 给string.zy、String( ).zy前缀扩展功能
extension ZY where Base == String {
var numberCount: Int {
var number = 0
for c in base where ("0"..."9").contains(c){
number += 1
}
return number
}
mutating func test() {
print("---test---")
}
static func staticTest() {
print("---static test---")
}
}
print(greeting.zy.numberCount)
greeting.zy.test()
String.zy.staticTest()