閉包表達式語法的一般形式：
{ (parameters) -> returnType in
statements
}```
####根據上下文推斷類型
通過內聯閉包表達式構造的閉包作為參數傳遞給函數或方法時，總是能夠推斷出閉包的參數和返回值類型。這意味著閉包作為函數或者方法的參數時，你幾乎不需要利用完整格式構造內聯閉包。
####單表達式閉包隱式返回
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
reversedNames = names.sorted(by: { s1, s2 in s1 > s2 } )
#####參數名稱縮寫
reversedNames = names.sorted(by: { $0 > $1 } )
#####閉包是引用類型
無論你將函數或閉包賦值給一個常量還是變量，你實際上都是將常量或變量的值設置為對應函數或閉包的引用。
var myClosure = oneClosure
let thisClosure = twoClosure
#####自動閉包
自動閉包是一種自動創建的閉包，用于包裝傳遞給函數作為參數的表達式。這種閉包不接受任何參數，當它被調用的時候，會返回被包裝在其中的表達式的值。
var customersInLine = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
print(customersInLine.count)
// 打印出 "5"
let customerProvider = { customersInLine.remove(at: 0) /* 這時不會執行*/}
print(customersInLine.count)
// 打印出 "5"
print("Now serving (customerProvider())!")
// Prints "Now serving Chris!"
print(customersInLine.count)
// 打印出 "4"
// customersInLine is ["Alex", "Ewa", "Barry", "Daniella"]
func serve(customer customerProvider: () -> String) {
print("Now serving (customerProvider())!")
}
serve(customer: { customersInLine.remove(at: 0) } )
// 打印出 "Now serving Alex!"
使用**@autoclosure**關鍵字讓你能夠省略閉包的花括號，用一個普通的表達式來代替顯式的閉包
// customersInLine is ["Alex", "Ewa", "Barry", "Daniella"]
func serve(customer customerProvider: () -> String) {
print("Now serving (customerProvider())!")
}
serve(customer: { customersInLine.remove(at: 0) } )
// 打印出 "Now serving Alex!"
如果你想讓一個自動閉包可以“逃逸”，則應該同時使用 @autoclosure 和 @escaping 屬性。
// customersInLine i= ["Barry", "Daniella"]
var customerProviders: [() -> String] = []
func collectCustomerProviders(_ customerProvider: @autoclosure @escaping () -> String) {
customerProviders.append(customerProvider)
}
collectCustomerProviders(customersInLine.remove(at: 0))
collectCustomerProviders(customersInLine.remove(at: 0))
print("Collected (customerProviders.count) closures.")
// 打印 "Collected 2 closures."
for customerProvider in customerProviders {
print("Now serving (customerProvider())!")
}
// 打印 "Now serving Barry!"
// 打印 "Now serving Daniella!"
