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  1. 886a7fb Go.mod and v1.0.0 by Mitchell Hashimoto · 4 months ago master v1.0.0
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Build Status Go Documentation

go-multierror is a package for Go that provides a mechanism for representing a list of error values as a single error.

This allows a function in Go to return an error that might actually be a list of errors. If the caller knows this, they can unwrap the list and access the errors. If the caller doesn't know, the error formats to a nice human-readable format.

go-multierror implements the errwrap interface so that it can be used with that library, as well.

Installation and Docs

Install using go get

Full documentation is available at


go-multierror is easy to use and purposely built to be unobtrusive in existing Go applications/libraries that may not be aware of it.

Building a list of errors

The Append function is used to create a list of errors. This function behaves a lot like the Go built-in append function: it doesn't matter if the first argument is nil, a multierror.Error, or any other error, the function behaves as you would expect.

var result error

if err := step1(); err != nil {
	result = multierror.Append(result, err)
if err := step2(); err != nil {
	result = multierror.Append(result, err)

return result

Customizing the formatting of the errors

By specifying a custom ErrorFormat, you can customize the format of the Error() string function:

var result *multierror.Error

// ... accumulate errors here, maybe using Append

if result != nil {
	result.ErrorFormat = func([]error) string {
		return "errors!"

Accessing the list of errors

multierror.Error implements error so if the caller doesn‘t know about multierror, it will work just fine. But if you’re aware a multierror might be returned, you can use type switches to access the list of errors:

if err := something(); err != nil {
	if merr, ok := err.(*multierror.Error); ok {
		// Use merr.Errors

Returning a multierror only if there are errors

If you build a multierror.Error, you can use the ErrorOrNil function to return an error implementation only if there are errors to return:

var result *multierror.Error

// ... accumulate errors here

// Return the `error` only if errors were added to the multierror, otherwise
// return nil since there are no errors.
return result.ErrorOrNil()