Common mistakes daily practice 01

1、defer and panic Use

package main

import "fmt"

func main() {
	// This question mainly tests defer and panic
	//defer After the function is executed ,panic Print before execution , Therefore, the printing sequence 
	// After printing 
	// Printing 
	// Before printing 
	//panic:  Departure is abnormal 
	defer_call()
}

func defer_call() {
	defer func () {
		fmt.Println(" Before printing ")
	}()
	defer func () {
		fmt.Println(" Printing ")
	}()
	defer func () {
		fmt.Println(" After printing ")
	}()
	panic(" Departure is abnormal ")
}

2、for range Key points of circulation

package main

import "fmt"

func main() {
	// This is mainly about pointer reference 
	//for range  A copy of each element is created during the loop 
	// therefore  m[key] = &val  It's all variables  val  The address of , So finally  map  The values of all elements in are variables  val  The address of , Because in the end  val  To be an assignment 3, All the outputs are 3.
	wrong()
	fmt.Println("---------------------------------")
	right()
}

func wrong() {
	slice := []int{0,1,2,3}
	m := make(map[int]*int)

	for k,v := range slice {
		m[k] = &v
	}

	for k,v := range m {
		fmt.Println(k,*v)
	}
}

func right() {
	slice := []int{0,1,2,3}
	m := make(map[int]*int)

	for k,v := range slice {
		value := v
		m[k] = &value
	}

	for k,v := range m {
		fmt.Println(k,*v)
	}
}