Golang中defer、闭包以及命名返回值

defer后面跟普通函数

package main

func main() {
    run()
}

func run() {
    name := "Paul"
    defer sayHello(name) 
    name = "John"
}

func sayHello(name string) {
    println("Hello " + name)
}
// Hello Paul 只是延缓执行，实参会按照正常顺序传入函数中

defer，return和未命名的返回值

package main

func main() {
    name := run()
    println("return: name = " + name) 
}

func run() (string) {
    name := "Paul"
    defer sayHello(&name)
    name = "John"
    return name
}

func sayHello(name *string) {
    *name = "George"
    println("Hello " + *name)
}
//Hello John  虽然实参提前传入，但是传入的是一个指针，最后执行拿到的是经过修改过的值
//Hello George
//return: name = John  未命名返回值，所以 defer 无法对返回的值进行操作的

defer、return 和命名的返回值

package main

func main() {
    name := run()
    println("return: name = " + name) 

func run() (x string) {
    name := "Paul"
    x = name
    defer sayHello(&x) 
    name = "John"
    return name
}

func sayHello(name *string) {
    println("Hello " + *name)
    *name = "George"
    println("Hello " + *name)
}
//Hello John
//Hello George
//return: name = George 因为使用命名返回值，所 defer 里面依然可以对 defer 进行操作

package main

func main() {
    name := run()
    println("return: name = " + name) 

func run() (x string) {
    name := "Paul"
    x = name
    defer sayHello(x)
    name = "John"
    return name
}

func sayHello(name string) {
    println("Hello " + name)
    name = "George"
    println("Hello " + name)
}
//Hello Paul  延迟执行但是按照程序顺序执行，传入的实参为 Paul 
//Hello George 函数内修改对外面的值没有影响
//return: name = John 

defer 闭包函数

package main

func main() {
    name := run()
    println("return: name = " + name)
}

func run() (string) {
    name := "Paul"
    aFun := func() {
        println("Hello " + name)
        name = "George"
        println("Hello " + name)
    }
    name = "John"
    aFun()
    return name
}
//Hello John 虽然闭包定义时，外部变量 name = "Paul", 但是其实只是记录是一个指针，所以最后执行的时候 name = "John" 
//Hello George
//return: name = George

package main

func main() {
    name := run()
    println("return: name = " + name)
}

func run() (x string) {
    name := "Paul"
    aFun := func() {
        println("Hello " + x)
        x = "George"
        println("Hello " + x)
    }
    defer aFun()
    name = "John"
    return name
}
//Hello John 
//Hello George
//return: name = George  defer 对返回值进行了修改

package main

func main() {
    name := run()
    println("return: name = " + name)
}

func run() (x string) {
    name := "Paul"
    x = name
    aFun := func(x string) {
        println("Hello " + x)
        x = "George"
        println("Hello " + x)
    }
    defer aFun(x)
    name = "John"
    return name
}
//Hello Paul  实参按照顺序拷贝传入 x = "Paul"
//Hello George 
//return: name = John  因为设置了形参所以闭包内的对应的变量只是在局部生效，不会影响外部变量