今天早上凌晨,苹果召开WWDC2017,想必大家都看了吧。新增的内容还是挺多的,特别是全新的CoreML
和ARKit
,非常期待我们能用这两个framework能做出点什么新的东西,后续会为大家带来与这两个相关的一些文章。
另外Swift 4也发布了,我大概看了下官方的更新日志,我整理了可能会比较常用的主要几点,完整的更新日志请点击这里 >>:
初始化一个多行字符串
可以直接在多行字符串中包含"
let quotation = """
The White Rabbit put on his spectacles. "Where shall I begin,
please your Majesty?" he asked.
"Begin at the beginning," the King said gravely, "and go on
till you come to the end; then stop."
"""
可以直接在多行字符串中包含"""
let threeDoubleQuotes = """
Escaping the first quote \"""
Escaping all three quotes \"\"\"
"""
以下两个字符串是等价的:
let singleLineString = "These are the same."
let multilineString = """
These are the same.
"""
在字符串前后加空行,可以这样写:
"""
This string starts with a line feed.
It also ends with a line feed.
"""
如果一个多行字符串定义在一个方法中,实际字符串的值是不包含每一行前面的空格:
func generateQuotation() -> String {
let quotation = """
The White Rabbit put on his spectacles. "Where shall I begin,
please your Majesty?" he asked.
"Begin at the beginning," the King said gravely, "and go on
till you come to the end; then stop."
"""
return quotation
}
print(quotation == generateQuotation())
// Prints "true"
如果把字符串改为下面的这个样子,第二行字符串前面的空格是不能忽略的:
func generateQuotation() -> String {
let quotation = """
The White Rabbit put on his spectacles. "Where shall I begin,
please your Majesty?" he asked.
"Begin at the beginning," the King said gravely, "and go on
till you come to the end; then stop."
"""
return quotation
}
print(quotation == generateQuotation())
// Prints "false"
泛型下标 (Generic Subscripts)
下标可以是泛型的,并且可以包含where
语句:
extension Container {
subscript(indices: Indices) -> [Item]
where Indices.Iterator.Element == Int {
var result = [Item]()
for index in indices {
result.append(self[index])
}
return result
}
}
上述代码的意思是:接受一个下标序列,并返回对应的元素组成的数组:
-
Indices
必须遵循Sequence
协议 -
indices
必须是Indices
类型 -
where
语句要求Indices
的元素必须是Int
类型
协议组合中可以包含父类
例如下面这个例子:
class Location {
var latitude: Double
var longitude: Double
init(latitude: Double, longitude: Double) {
self.latitude = latitude
self.longitude = longitude
}
}
class City: Location, Named {
var name: String
init(name: String, latitude: Double, longitude: Double) {
self.name = name
super.init(latitude: latitude, longitude: longitude)
}
}
func beginConcert(in location: Location & Named) {
print("Hello, \(location.name)!")
}
let seattle = City(name: "Seattle", latitude: 47.6, longitude: -122.3)
beginConcert(in: seattle)
// Prints "Hello, Seattle!"
在beginConcert
方法中,location
参数必须Location
类型,并且遵循Named
协议。
final
关键字不能用在协议扩展中
在协议扩展里面,我们不能使用final
。
Swift 3中,在extension访问private属性会报错;而在Swift 4中,允许我们这么做。
1.jpg
Xcode 9可以自定义编译器的Swift版本
2.jpg
Xcode 9集成新的编译系统,编译速度更快
3.jpg
在Swift和OC混编时,我们要使用bridging headers,Xcode9可以预编译 bridging headers,大幅度减少编译时间,apple music的编译速度提高40%
在访问字符串的index时,不用再写value.characters.startIndex
,直接写成value.startIndex
即可
访问字符串的从中间某个index到endIndex的字符,可以省略endIndex
不允许在遍历数组的时候,修改当前遍历的数组
完
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