元组（tuples）
把多个值组合成一个复合值。元组内的值可以是任意类型，并不要求是相同类型
let http404Error = (404, "Not Found")
let (statusCode, statusMessage) = http404Error
print("The status code is (statusCode)")
print("The status message is (statusMessage)")
忽略后面的值
let (justTheStatusCode, _) = http404Error
print("The status code is (justTheStatusCode)")
通过下标来访问元组中的单个元素
print("The status code is (http404Error.0)")
可以在定义元组的时候给单个元素命名
let http200Status = (statusCode: 200, description: "OK")
print("The status code is (http200Status.statusCode)")
断言
let age = -3
assert(age >= 0, "A person's age cannot be less than zero")
会导致程序的终止
错误处理
func makeASandwich() throws {
// ...
}
do {
try makeASandwich()
eatASandwich()
} catch SandwichError.outOfCleanDishes {
washDishes()
} catch SandwichError.missingIngredients(let ingredients) {
buyGroceries(ingredients)
}