go 函数小结

函数

defer

go语言中函数的return不是原子操作，在底层分为两层操作

第一步：返回值赋值

defer

第二步：真正的ret返回

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func f1() int {
    x := 5
    defer func() {
        x++
    }()
    return x
}

func f2() (x int) {
    defer func() {
        x++
    }()
    return 5
}

func f3() (y int) {
    x := 5
    defer func() {
        x++
    }()
    return x
}
func f4() (x int) {
    defer func(x int) {
        x++
    }(x)
    return 5
}
func f5()(x int){
    defer func(x int) int{
        x++
        return x
    }(x)
    return 5
}

func f6(x int){
    defer func(x *int){
        (*x)++
    }(*x)
    return 5
}
func main() {
    fmt.Println(f1())   //5
    fmt.Println(f2())   //6
    fmt.Println(f3())   //5 
    fmt.Println(f4())   //5
    fmt.Println(f5())   //5 
    fmt.Println(f6())   //6
}

defer 会将值先赋值到函数中

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func main(){
    a := 1
	b := 2
	defer calc("1", a, calc("10", a, b))
	a = 0
	defer calc("2", a, calc("20", a, b))
	b = 1
}
    
	
func calc(index string, a, b int) int{
	ret := a +b
	fmt.Println(index, a, b, ret)
	// 20 0 1
	// 2 0 1
	// 10 0 1
	// 1 0 1
	return ret
}

----------------
10 1 2 3
20 0 2 2
2 0 2 2
1 1 3 4

闭包

例如：

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func f11(f func()){
	fmt.Println("this is f1")
	f()
}

func f22(x, y int) {
	fmt.Println("this is f2")
	fmt.Println(x + y)
}

func f33(f func(int, int), x, y int) func(){
	tmp := func(){
		f(x, y)
	}
	return tmp
}
//实现f1(f2)
func main(){
    ret := f33(f22, 100, 200)
    	f11(ret)
}
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func adder() func(int) int {
	var x int
	return func(y int) int {
		x += y
		return x
	}
}
func main() {
	var f = adder()
	fmt.Println(f(10)) //10
	fmt.Println(f(20)) //30
	fmt.Println(f(30)) //60

	f1 := adder()
	fmt.Println(f1(40)) //40
	fmt.Println(f1(50)) //90
}
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func calc(base int) (func(int) int, func(int) int) {
	add := func(i int) int {
		base += i
		return base
	}

	sub := func(i int) int {
		base -= i
		return base
	}
	return add, sub
}

func main() {
	f1, f2 := calc(10)
	fmt.Println(f1(1), f2(2)) //11 9
	fmt.Println(f1(3), f2(4)) //12 8
	fmt.Println(f1(5), f2(6)) //13 7
}

1、

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func calc(index string, a, b int) int {
	ret := a + b
	fmt.Println(index, a, b, ret)
	return ret
}

func main() {
	x := 1
	y := 2
	defer calc("AA", x, calc("A", x, y))
	x = 10
	defer calc("BB", x, calc("B", x, y))
	y = 20
}

上面代码的输出结果是?