Yet another Go MultiError

multierror.go

package main

import (
	"fmt"
	"strings"
)

// MultiError implements the Error interface, can be checked as nil just like normal errors.
func MultiError() multiError {
	var err multiError = nil
	return err
}

type multiError []error

func (e *multiError) Add(err error) {
	if err == nil {
		return
	}
	if e == nil {
		*e = []error{err}
		return
	}
	*e = append(*e, err)
}

func (e multiError) Error() string {
	if len(e) == 0 {
		return ""
	}
	if len(e) == 1 {
		return e[0].Error()
	}
	s := make([]string, 0, len(e)+1)
	s = append(s, fmt.Sprintf("%d errors:", len(e)))
	for _, err := range e {
		s = append(s, " * "+err.Error())
	}
	return strings.Join(s, "\n")
}