Go - Raise an exception

Question

I would want to raise an exception as it's made in Python or Java --to finish the program with an error message--.

An error message could be returned to a parent function:

func readFile(filename string) (content string, err os.Error) {
    content, err := ioutil.ReadFile(filename)
    if err != nil {
        return "", os.ErrorString("read " + filename + ": " + err)
    }
    return string(content), nil
}

but I want that it can be finished when the error is found. Would be correct the next one?

func readFile(filename string) (content string) {
    content, err := ioutil.ReadFile(filename)

    defer func() {
        if err != nil {
            panic(err)
        }
    }()

    return string(content)
}

Answer 1

In java, in your application main function:

public class App 
    public static void main(String[] args) { 
        try { 
           // logic
        } catch ( ExitProgramException ex) { 
           // exit program
        } 
    }
}

Then throw ExitProgramException whenever you want to forcibly exit the program.

You could event craft an exception that overrides ExitProgramException.toString() -> it prints itself to the console and then forcibly exits with System.exit();

I wouldn't advise it, but it's possible.

Answer 2

By convention, Go doesn't do things like this. It has panic and recover, which are sort of exception-like, but they're only used in really exceptional circumstances. Not finding a file or similar is not an exceptional circumstance at all, but a very regular one. Exceptional circumstances are things like dereferencing a nil pointer or dividing by zero.