Go: returning from defer

Question

I want to return an error from a function if it panics (in Go):

func getReport(filename string) (rep report, err error) {     rep.data = make(map[string]float64)      defer func() {         if r := recover(); r != nil {             fmt.Println("Recovered in f", r)             err, _ = r.(error)             return nil, err         }     }()     panic("Report format not recognized.")     // rest of the getReport function, which can try to out-of-bound-access a slice     ... }  

I appear to have misunderstood the very concept of panic and defer. Can anybody enlighten me?

Answer 1

In a deferred function you can alter the returned parameters, but you can't return a new set. So a simple change to what you have will make it work.

There is another problem with what you wrote, namely that the you've paniced with a string but are expecting an error in your type assertion.

Here is a fix for both of those (Play)

defer func() {     if r := recover(); r != nil {         fmt.Println("Recovered in f", r)         // find out exactly what the error was and set err         switch x := r.(type) {         case string:             err = errors.New(x)         case error:             err = x         default:             err = errors.New("Unknown panic")         }         // invalidate rep         rep = nil         // return the modified err and rep     } }()