Go: Error
error object is returned.
func divide(number1, number2 int) (int, error) {
if number2 == 0 {
return 0, errors.New("cannot divide by 0")
}
return number1/number2, nil
}
func main() {
result,err := divide(1,2)
if err != nil {
log.Fatal(err)
}
fmt.Println(result)
}
// This interface needs to be implemented
/*
type error interface {
Error() string
}
*/
type DivideByZeroErr struct{
num1 int
num2 int
}
func (err *DivideByZeroErr) Error() string {
return fmt.Sprintf("cannot divide %d by 0", err.num1)
}
func divide(number1, number2 int) (int, error) {
if number2 == 0 {
return 0, &DivideByZeroErr{number1, number2}
}
return number1/number2, nil
}
func main() {
result,err := divide(1,0)
if err != nil {
log.Fatal(err)
}
fmt.Println(result)
}
// output
// cannot divide 1 by 0
Basically when an error occurs there is a situation where one would want the application to stop if not succeeded. some use cases are, Initially making database connection or initializing something for app to run and it fails.
Example: func MustCompile(str string) *Regexp 2
With the use of use case specific OBJECT_TYPE (replace OBJECT_TYPE with your required return type)
func Must(obj OBJECT_TYPE, err error) OBJECT_TYPE {
if err != nil {
panic(err)
}
return obj
}
With the use of generics 3
func Must[T any](obj T, err error) T {
if err != nil {
panic(err)
}
return obj
}
package main
import "fmt"
func causePanic() {
panic("something went terribly wrong")
}
func main() {
fmt.Println("Before panic")
causePanic()
fmt.Println("After panic") // This line won't be executed
}
Defer will run before panic
package main
import "fmt"
func causePanic() {
panic("something went terribly wrong")
}
func main() {
defer func() {
fmt.Println("Ran before panic")
}()
fmt.Println("Before panic")
causePanic()
fmt.Println("After panic") // This line won't be executed
}
package main
import "fmt"
func safeFunction() {
defer func() {
if r := recover(); r != nil {
fmt.Println("Recovered from panic:", r)
}
}()
panic("unexpected error")
}
func main() {
safeFunction()
fmt.Println("Program continues after recovery")
}
Output:
Recovered from panic: unexpected error
Program continues after recovery
package main
import "fmt"
func main() {
defer handlePanic() // recover is here, not in riskyFunction
riskyFunction()
fmt.Println("Program continues after recovery")
}
func panicInsideRiskyFunction() {
panic("something went wrong in panicInsideRiskyFunction")
}
func riskyFunction() {
panicInsideRiskyFunction()
}
func handlePanic() {
if r := recover(); r != nil {
fmt.Println("Recovered from panic:", r)
}
}
Output:
Recovered from panic: something went wrong in panicInsideRiskyFunction
package main
import (
"fmt"
)
func run() (errP error) {
defer func() {
err := recover()
if err != nil {
errP = fmt.Errorf("Error recover: %s", err)
}
}()
panic("A panic occurred")
return nil
}
func main() {
err := run()
if err != nil {
fmt.Println("error from run", err)
}
}
error from run Error recover: A panic occurred
package main
import (
"fmt"
)
func run() (errP error) {
defer func() {
err := recover()
if err != nil {
errP = fmt.Errorf("Error recover: %s", err)
}
panic("panic inside recover")
}()
panic("A panic occurred")
return nil
}
func main() {
err := run()
if err != nil {
fmt.Println("error from run", err)
}
}
panic: A panic occurred [recovered]
panic: panic inside recover
goroutine 1 [running]:
main.run.func1()
/panic.go:13 +0x3d
panic({0x49b740?, 0x4d7970?})
/usr/local/go/src/runtime/panic.go:785 +0x132
main.run()
/panic.go:15 +0x58
main.main()
/panic.go:20 +0x13
exit status 2