Go programs express error state with error values.
The error type is a built-in interface similar to fmt.Stringer:

type error interface {
    Error() string

A nil error denotes success; a non-nil error denotes failure.

Functions often return an error value, and calling code should handle errors by testing whether the error equals nil.

i, err := strconv.Atoi("42")
if err != nil {
    fmt.Printf("couldn't convert number: %v\n", err)
fmt.Println("Converted integer:", i)

Error Wrapping

var criticalError = errors.New("Serious error")
unwrapped = fmt.Errorf("...%w...", criticalError)


Go makes it possible to recover from a panic, by using the recover built-in function. A recover can stop a panic from aborting the program and let it continue with execution instead.

package main
import "fmt"
func mayPanic() {
    panic("a problem")
func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered. Error:\n", r)
    fmt.Println("After mayPanic()")

Under the hood, recover takes effect after panic, so put it in defer.