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

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