Error handling best practice

Go has two different error-handling mechanisms:

• most functions return errors;
• only a truly unrecoverable condition, such as an out-of-range index, produces a run-time exception, known as a panic.

Go’s multivalued return makes it easy to return a detailed error message alongside the normal return value. By convention, such messages have type error, a simple built-in interface:

type error interface {
    Error() string
}

Error handling example

The os.Open function returns a non-nil error value when it fails to open a file.

func Open(name string) (file *File, err error)

The following code uses os.Open to open a file. If an error occurs it calls log.Fatal to print the error message and stop.

f, err := os.Open("filename.ext")
if err != nil {
    log.Fatal(err)
}
// do something with the open *File f

Custom errors

To create a simple string-only error you can use errors.New:

err := errors.New("Houston, we have a problem")

The error interface requires only an Error method, but specific error implementations often have additional methods, allowing callers to inspect the details of the error.

Learn more

Panic

Panics are similar to C++ and Java exceptions, but are only intended for run-time errors, such as following a nil pointer or attempting to index an array out of bounds.

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