golang中defer执行时机的案例分析

package main
import "fmt"

func calcFunc(x int, y int) int {
	return x + y
}

func main() {
	// defer语句的执行顺序是，从右到左,逆序执行
	deferDemo()

	// deferDemo1函数
	demo1 := deferDemo1()
	fmt.Println(demo1) // 0

	// deferDemo2函数
	demo2 := deferDemo2()
	fmt.Println(demo2) // 1

	// deferDemo4
	demo4 := deferDemo4()
	fmt.Println(demo4) // 1

	// deferDemo5
	demo5 := deferDemo5()
	fmt.Println(demo5) // 1

	// deferDemo6
	demo6 := deferDemo6()
	fmt.Println(demo6) // 2

	// 难点解析
	/*
		   分析:
			defer注册顺序:
			1.defer fmt.Println("AA", calcFunc(x, calcFunc(x, y)))
			2.defer fmt.Println("BB", calcFunc(x, calcFunc(x, y)))
			defer执行顺序:
			1. fmt.Println("BB", calcFunc(x, calcFunc(x, y)))
			2. fmt.Println("AA", calcFunc(x, calcFunc(x, y)))

	*/
	x := 1
	y := 2
	// 注册的时候 x = 1, y = 2 所以执行的时候x = 1, y = 2
	defer fmt.Println("AA", calcFunc(x, calcFunc(x, y))) // calcFunc(1,1+2)  // 结果是:4
	x = 10
	// 注册的时候x = 10, y = 2 所以执行的时候x = 10, y = 2
	defer fmt.Println("BB", calcFunc(x, calcFunc(x, y))) // calcFunc(10,10+2) // 结果是:22
	y = 20

}

func deferDemo() {
	fmt.Println("开启defer")
	defer func() {
		fmt.Println("defer语句1")
	}()
	defer func() {
		fmt.Println("defer语句2")
	}()
	defer func() {
		fmt.Println("defer语句3")
	}()

	defer fmt.Println("defer语句4")
	defer fmt.Println("defer语句5")
	defer fmt.Println("defer语句6")

	fmt.Println("结束defer")
}

func deferDemo1() int {
	var a int

	defer func() {
		a++
	}()

	return a
}

func deferDemo2() (a int) {
	// 步骤一先赋值
	//a = 0

	// 步骤二再执行defer语句
	defer func() {
		a++
	}()

	// 步骤三再执行函数体
	// 返回值a等待函数体内操作完成才会执行return
	return a
}

func deferDemo3() (a int) {
	defer func() {
		a++
	}()

	return a
}

func deferDemo4() int {
	x := 1

	defer func(x int) {
		x++ // 内部x和外面x不是同一个变量
	}(x)

	return x // 1
}

func deferDemo5() (x int) {
	x = 1

	defer func(x int) {
		x++ // 内部x和外面x不是同一个变量
	}(x)

	return x // 1
}

func deferDemo6() (x int) {
	x = 1

	defer func() {
		x++
	}()

	return x // 2
}