Error handling vs. exceptions redux

Revisiting my post about error handling and exceptions, written well before Go hit 1.0, I’m pleased that it stands the test of time.

Java has comprehensively demonstrated that checked exceptions (actually having both checked and unchecked exceptions) has been a disaster for the evolution of the language.

Checked exceptions have placed a suffocating yoke of backward compatibility on the architects trying to modernise Java’s decades old design.

I can see no future language designers making the same decision, no matter how well meaning, as the Java designers in 1995.

C++ exceptions, remain as difficult to use safely as they did three decades ago. When any part of your call stack can explode without warning, it is no wonder so many C++ shops mandate that exceptions not be used.

Where does this leave Go, with its sometimes long winded, but always predictable error values?

Two things

The first is an observation made by Rob Pike at Gophercon 2014

Error values in Go aren’t special, they are just values like any other, and so you have the entire language at your disposal.

I think this is something so fundamental that it escapes the notice of most Go programmers.

The second, which I ran across a close to a year after my first post, was this presentation by Andrei Alexandrescu, where he noted (around the 11 minute mark):

… exceptional code is hopelessly serial. There is only one exception in flight, how quaint is that ? There can be only one exception at any moment in flight. … [they] require immediate an exclusive attention. [The exception] comes to the fore, you must handle it right now.

To me this is the argument that seals the case in the favour of errors over exceptions.

Consider this simple example that consumes the contents of an io.Reader.

func ReadAll(r io.Reader) ([]byte, error) {
        var buf = make([]byte, 1024)
        var result []byte
        for {
                n, err := r.Read(buf)
                result = append(result, buf[:n]...)
                if err == io.EOF {
                        return result, nil
                if err != nil {
                        return nil, err

In Go, handling any returned data, as well as an error, is second nature. I cannot begin to think of how you could handle this as simply in an exception based workflow.


Everything that I wrote then, nearly three years ago, I believe to be true today. So in conclusion, stealing a line from Churchill,

Returning error values is the worst form of error handling, except all the others that have been tried.