Go 언어에서 defer, panic

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
)

func main() {
	res, err := http.Get("http://www.google.com/robots.txt")
	if err != nil {
		log.Fatal(err)
	}

	defer res.Body.Close() // leave the defer keyword off, you do get an error
	robots, err := ioutil.ReadAll(res.Body)

	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%s", robots)
}


// 결과
//
// ...
// User-agent: facebookexternalhit
// Allow: /imgres
//
// Sitemap: https://www.google.com/sitemap.xml

---

package main

import (
	"fmt"
)

func main() {
	s := "start"
	defer fmt.Println(s)
	s = "end"
}

// 결과
//
// start

---

package main

import (
	"fmt"
)

func main() {
	x, y := 1, 0
	ret := x / y

	fmt.Println(ret)
}

// 결과
//
// panic: runtime error: integer divide by zero

package main

import (
	"net/http"
)

func main() {
	// basic web handler
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Hello Go!"))
	})

	err := http.ListenAndServe(":8080", nil)
	if err != nil {
		panic(err.Error())
	}
}

---

• any deferred call to close resources are still going to work even if a function panics

package main

import (
	"fmt"
)

func main() {
	fmt.Println("start")
	defer fmt.Println("this was deferred")
	panic("something bad changed")
	fmt.Println("end")
}

// 결과
//
// start
// this was deferred
// panic: something bad changed

---

package main

import (
	"fmt"
	"log"
)

func main() {
	fmt.Println("start")
	panicker()
	fmt.Println("end")
}

func panicker() {
	fmt.Println("about to panic")
	defer func() {
		if err := recover(); err != nil {
			log.Println("Error:", err)
		}
	}()
	panic("something bad happened")
	fmt.Println("done panicking")
}

// 결과
//
// start
// about to panic
// 2022/03/17 07:22:13 Error: something bad happened
// end