Use three double quotes (""") for strings that take up multiple lines
使用三个双引号，标示跨越多行的字符串
let quotation = """
Even though there's whitespace to the left,
the actual lines aren't indented.
Except for this line.
Double quotes (") can appear without being escaped.
I still have \(apples + oranges) pieces of fruit.
"""Another way to handle optional values is to provide a default value using the ?? operator. If the optional value is missing, the default value is used instead.
另外一种处理可选值的方式是用 ?? 运算符 如果一个可选值不存在值，则使用默认值代替
let nickName: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickName ?? fullName)"Notice how let can be used in a pattern to assign the value that matched the pattern to a constant.
可以使用let 在switch里进行一个模式匹配
let vegetable = "red pepper"
switch vegetable {
case "celery":
print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
print("Is it a spicy \(x)?")
default:
print("Everything tastes good in soup.")
}In an if statement, the conditional must be a Boolean expression—this means that code such as if score { ... } is an error, not an implicit comparison to zero. 与0没有什么关系
You use for-in to iterate over items in a dictionary by providing a pair of names to use for each key-value pair. Dictionaries are an unordered collection, so their keys and values are iterated over in an arbitrary order.
（key, value）
let interestingNumbers = [
"Prime": [2, 3, 5, 7, 11, 13],
"Fibonacci": [1, 1, 2, 3, 5, 8],
"Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
for number in numbers {
if number > largest {
largest = number
}
}
}
print(largest)Use while to repeat a block of code until a condition changes. The condition of a loop can be at the end instead, ensuring that the loop is run at least once.
类似do while
var m = 2
repeat {
m *= 2
} while m < 100
print(m)You can keep an index in a loop by using ..< to make a range of indexes.
Use ..< to make a range that omits its upper value, and use ... to make a range that includes both values.
var total = 0
for i in 0..<4 {
total += i
}
print(total)By default, functions use their parameter names as labels for their arguments. Write a custom argument label before the parameter name, or write _ to use no argument label.
参数的外部名称和内部名称
func greet(_ person: String, on day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet("John", on: "Wednesday")tuple 下标从0开始
Use a tuple to make a compound value—for example, to return multiple values from a function. The elements of a tuple can be referred to either by name or by number.
func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
var min = scores[0]
var max = scores[0]
var sum = 0
for score in scores {
if score > max {
max = score
} else if score < min {
min = score
}
sum += score
}
return (min, max, sum)
}
let statistics = calculateStatistics(scores: [5, 3, 100, 3, 9])
print(statistics.sum)
print(statistics.2)函数可以嵌套
Functions can be nested. Nested functions have access to variables that were declared in the outer function. You can use nested functions to organize the code in a function that is long or complex.
func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()Functions are a first-class type. This means that a function can return another function as its value.
函数本身可以作为一种类型返回，非常灵活
func makeIncrementer() -> ((Int) -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)A function can take another function as one of its arguments.
当然也能作为参数
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(list: numbers, condition: lessThanTen)
