七、泛型
func swapTwoInts(_ a:inout Int, _ b:inout Int) {
let temp = a
a = b
b = temp
}
func swaoTwoValues<T>(_ a:inout T, _ b:inout T) {
let temp = a
a = b
b = temp
}
var a = 13, b = 12
swapTwoInts(&a, &b)
print(a, b)
var aStr = "12", bStr = "333"
//swapTwoInts(&aStr, &bStr)
swaoTwoValues(&a, &b)
print(a, b)
swaoTwoValues(&aStr, &bStr)
print(aStr, bStr)
// 上面的🌰中,swapTwoInts只能交换Int类型的值,而后面声明的泛型swaoTwoValues可以交换不同类型的值,更简洁
struct Stack<Element> {
var items = [Element]()
mutating func push(_ item: Element) {
items.append(item)
}
mutating func pop() -> Element {
return items.removeLast()
}
}
// 初始化的时候类型不能省略Stack<String>()
var stackOfStrings = Stack<String>()
stackOfStrings.push("ddd")
stackOfStrings.push("jdieji")
stackOfStrings.push("d")
stackOfStrings.pop()
// 上面的🌰中,声明了一个泛型栈
//当你扩展一个泛型类型时,不需要在扩展的定义中提供类型形式参数列表。原始类型定义的类型形式参数列表在扩展体里仍然有效,并且原始类型形式参数列表名称也用于扩展类型形式参数。
extension Stack {
var topItem: Element? {
return items.isEmpty ? nil : items[items.count - 1]
}
}
// 类型约束
/*
func somFunction<T: SomeClass, U: SomeProtocol>(someT: T, someU: U) {
// func body
}
*/
func findIndex<T: Equatable>(of valueToFind: T, in array:[T]) -> Int? {
for (index, value) in array.enumerated() {
if value == valueToFind {
return index
}
}
return nil
}
// 关联类型(协议使用泛型)
protocol Container {
associatedtype ItemType
mutating func append(_ item: ItemType)
var count: Int { get }
subscript(i: Int) -> ItemType { get }
}
struct IntStack: Container {
var items = [Int]()
// 通过强大的类型推断,类型可以省略
typealias ItemType = Int
mutating func append(_ item: Int) {
items.append(item)
}
var count: Int {
return items.count
}
subscript(i: Int) -> Int {
return items[i]
}
}
// 泛型+where
func allItemsMAtch<C1: Container, C2: Container>(_ someContainer: C1, _ anotherContainer: C2) -> Bool where C1.ItemType == C2.ItemType, C1.ItemType: Equatable {
if someContainer.count != anotherContainer.count {
return false
}
for i in 0..<someContainer.count {
if someContainer[i] != anotherContainer[i]
return false
}
return true
}
//extension Stack wherr Element : Equatable {
// // code
//}
extension Container where ItemType: Equatable {
// code
}
extension Container where ItemType == Double {
// code
}
// 泛型下标
extension Container {
subscript<Indices: Sequence>(indics: Indices) -> [ItemType] where Indices.Iterator.Element == Int {
var result = [ItemType]()
for index in indics {
result.append(self[index])
}
return result
}
}
struct IntStack: Container {
var items = [Int]()
// 通过强大的类型推断,类型可以省略
typealias ItemType = Int
mutating func append(_ item: Int) {
items.append(item)
}
var count: Int {
return items.count
}
subscript(i: Int) -> Int {
return items[i]
}
}
var intStack = IntStack()
intStack.append(1)
intStack.append(2)
print(intStack[[0, 1]])