Panic
fmt osA panic typically means something went unexpectedly wrong. Mostly we use it to fail fast on errors that shouldn't occur during normal operation, or that we aren't prepared to handle gracefully.
package main
import (
"fmt"
"os"
)check panics on any error. A helper like this is fine in small scripts, but real programs should return errors instead.
func check(err error) {
if err != nil {
panic(err)
}
}
func main() {
fmt.Println("about to create a file in a directory that does not exist")A common use of panic is to abort if a function returns an error value that we don't know how to (or want to) handle. Here's an example of panicking if we get an unexpected error when creating a new file. panic also accepts any value, such as panic("a problem").
_, err := os.Create("/no/such/dir/file")
check(err)Running this program causes it to panic, print an error message and goroutine traces, and exit with a non-zero status. When the panic fires, the program exits without reaching the rest of the code. Note that unlike some languages which use exceptions for handling of many errors, in Go it is idiomatic to use error-indicating return values wherever possible.
fmt.Println("never printed")
}$ go run ./29_panic about to create a file in a directory that does not exist panic: open /no/such/dir/file: no such file or directory goroutine 1 [running]: main.check(...) ./29_panic/main.go:19 main.main() ./29_panic/main.go:31 +0xb7 exit status 2