Confusing defer, return, named return value, anonymous return value in golang

demo01

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println(1)
	fmt.Println(2)
	fmt.Println(3)
	fmt.Println(" end ")
}

Print ：

 Start 
1
2
3
 end 

demo02

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	defer fmt.Println(1)
	defer fmt.Println(2)
	defer fmt.Println(3)
	fmt.Println(" end ")
}

Print ：

 Start 
 end 
3
2
1

demo03

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println("f1 Return results ：",f1())
	fmt.Println(" end ")
}
func f1() int {
    
	var a int
	defer func() {
    
		a++
	}()
	return a
}

 Start 
f1 Return results ： 0
 end 

demo04

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println("f1 Return results ：",f1())
	fmt.Println(" end ")
}
func f1() (a int) {
    

	defer func() {
    
		a++
	}()
	return a
}

 Start 
f1 Return results ： 1
 end 

demo05

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println("f1 Return results ：", f1())
	fmt.Println(" end ")
}
func f1()  ( a int) {
    
	defer func() {
    
		a++
	}()
	return 5
}

 Start 
f1 Return results ： 6
 end 

demo06

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println("f1 Return results ：", f1())
	fmt.Println(" end ")
}
func f1()  ( y int) {
    
	x:=5
	defer func() {
    
		x++
	}()
	return x
}

 Start 
f1 Return results ： 5
 end 

demo07

package main

import "fmt"

func main() {
    
	fmt.Println(" Start ")
	fmt.Println("f1 Return results ：", f1())
	fmt.Println(" end ")
}
func f1()  ( x int) {
    
	defer func(x int) {
    
		x++
	}(x)
	return 5
}

 Start 
f1 Return results ： 5
 end 

demo08

package main

import (
	"fmt"
)

func main() {
    
	fmt.Println("test Execution results :", test(test1))

}

func test(fn func() error) int {
    
	a := 1000
	fmt.Println("a:", a)
	defer func() {
    
		if p := recover(); p != nil {
    
			a = 2
			fmt.Println("error occur")
		}
	}()
	_ = fn()
	fmt.Println("999999")
	return a
}
func test1() error {
    
	panic("ha")
	return nil
}

a: 1000
error occur
test Execution results : 0

demo09

package main

import "fmt"

/** * @author micro.cloud.fly * @date 2022/3/4 11:39  In the morning  * @desc */
func main() {
    
	x := 1
	y := 2
	defer fmt.Println(calc("AA", x, calc("a", x, y)))
	x = 10
	defer fmt.Println(calc("BB", x, calc("b", x, y)))
	y = 20

}
func calc(flag string, x, y int) int {
    
	fmt.Println(flag, x, y, x+y)
	return x + y
}

defer At registration time , All parameters must be determined , For details, see https://www.bilibili.com/video/BV1x5411h7Md?p=28

a 1 2 3
AA 1 3 4
b 10 2 12
BB 10 12 22
22
4