Swift中文教程2
2014-06-05 18:50
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函数和闭包
函数
Swift使用func关键字声明函数:
func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")
通过元组(Tuple)返回多个值:
func getGasPrices() -> (Double, Double, Double) {
return (3.59, 3.69, 3.79)
}
getGasPrices()
支持带有变长参数的函数:
func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(42, 597, 12)
函数也可以嵌套函数:
func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()
作为头等对象,函数既可以作为返回值,也可以作为参数传递:
func makeIncrementer() -> (Int -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {
for item in list {
if condition(item) {
return true
}
}
return false
}
func lessThanTen(number: Int) -> Bool {
return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(numbers, lessThanTen)
闭包
本质来说,函数是特殊的闭包,Swift中可以利用{}声明匿名闭包:
numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})
当闭包的类型已知时,可以使用下面的简化写法:
numbers.map({ number in 3 * number })
此外还可以通过参数的位置来使用参数,当函数最后一个参数是闭包时,可以使用下面的语法:
sort([1, 5, 3, 12, 2]) { $0 > $1 } 类和对象 创建和使用类
Swift使用class创建一个类,类可以包含字段和方法:
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
创建Shape类的实例,并调用其字段和方法。
var shape = Shape()
shape.numberOfSides = 7
varshapeDescription = shape.simpleDescription()
通过init构建对象,既可以使用self显式引用成员字段(name),也可以隐式引用(numberOfSides)。
class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
使用deinit进行清理工作。
继承和多态
Swift支持继承和多态(override父类方法):
class Square: NamedShape {
var sideLength: Double
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() -> Double {
return sideLength * sideLength
}
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
}
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()
注意:如果这里的simpleDescription方法没有被标识为override,则会引发编译错误。
属性
为了简化代码,Swift引入了属性(property),见下面的perimeter字段:
class EquilateralTriangle: NamedShape {
var sideLength: Double = 0.0
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 3
}
var perimeter: Double {
get {
return 3.0 * sideLength
}
set {
sideLength = newValue / 3.0
}
}
override func simpleDescription() -> String {
return "An equilateral triagle with sides of length \(sideLength)."
}
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
triangle.perimeter
triangle.perimeter = 9.9
triangle.sideLength
注意:赋值器(setter)中,接收的值被自动命名为newValue。
willSet和didSet
EquilateralTriangle的构造器进行了如下操作:
为子类型的属性赋值。 调用父类型的构造器。 修改父类型的属性。
如果不需要计算属性的值,但需要在赋值前后进行一些操作的话,使用willSet和didSet:
class TriangleAndSquare {
var triangle: EquilateralTriangle {
willSet {
square.sideLength = newValue.sideLength
}
}
var square: Square {
willSet {
triangle.sideLength = newValue.sideLength
}
}
init(size: Double, name: String) {
square = Square(sideLength: size, name: name)
triangle = EquilateralTriangle(sideLength: size, name: name)
}
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
triangleAndSquare.square.sideLength
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
triangleAndSquare.triangle.sideLength
从而保证triangle和square拥有相等的sideLength。
函数
Swift使用func关键字声明函数:
func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")
通过元组(Tuple)返回多个值:
func getGasPrices() -> (Double, Double, Double) {
return (3.59, 3.69, 3.79)
}
getGasPrices()
支持带有变长参数的函数:
func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(42, 597, 12)
函数也可以嵌套函数:
func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()
作为头等对象,函数既可以作为返回值,也可以作为参数传递:
func makeIncrementer() -> (Int -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {
for item in list {
if condition(item) {
return true
}
}
return false
}
func lessThanTen(number: Int) -> Bool {
return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(numbers, lessThanTen)
闭包
本质来说,函数是特殊的闭包,Swift中可以利用{}声明匿名闭包:
numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})
当闭包的类型已知时,可以使用下面的简化写法:
numbers.map({ number in 3 * number })
此外还可以通过参数的位置来使用参数,当函数最后一个参数是闭包时,可以使用下面的语法:
sort([1, 5, 3, 12, 2]) { $0 > $1 } 类和对象 创建和使用类
Swift使用class创建一个类,类可以包含字段和方法:
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
创建Shape类的实例,并调用其字段和方法。
var shape = Shape()
shape.numberOfSides = 7
varshapeDescription = shape.simpleDescription()
通过init构建对象,既可以使用self显式引用成员字段(name),也可以隐式引用(numberOfSides)。
class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
使用deinit进行清理工作。
继承和多态
Swift支持继承和多态(override父类方法):
class Square: NamedShape {
var sideLength: Double
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() -> Double {
return sideLength * sideLength
}
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
}
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()
注意:如果这里的simpleDescription方法没有被标识为override,则会引发编译错误。
属性
为了简化代码,Swift引入了属性(property),见下面的perimeter字段:
class EquilateralTriangle: NamedShape {
var sideLength: Double = 0.0
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 3
}
var perimeter: Double {
get {
return 3.0 * sideLength
}
set {
sideLength = newValue / 3.0
}
}
override func simpleDescription() -> String {
return "An equilateral triagle with sides of length \(sideLength)."
}
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
triangle.perimeter
triangle.perimeter = 9.9
triangle.sideLength
注意:赋值器(setter)中,接收的值被自动命名为newValue。
willSet和didSet
EquilateralTriangle的构造器进行了如下操作:
为子类型的属性赋值。 调用父类型的构造器。 修改父类型的属性。
如果不需要计算属性的值,但需要在赋值前后进行一些操作的话,使用willSet和didSet:
class TriangleAndSquare {
var triangle: EquilateralTriangle {
willSet {
square.sideLength = newValue.sideLength
}
}
var square: Square {
willSet {
triangle.sideLength = newValue.sideLength
}
}
init(size: Double, name: String) {
square = Square(sideLength: size, name: name)
triangle = EquilateralTriangle(sideLength: size, name: name)
}
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
triangleAndSquare.square.sideLength
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
triangleAndSquare.triangle.sideLength
从而保证triangle和square拥有相等的sideLength。
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