You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: be_an_existing_file.go
    path of file: ./repos/hoverfly/vendor/github.com/onsi/gomega/matchers
    
    the code of the file until where you have to start completion: // untested sections: 3

package matchers

import (
	"fmt"
	"os"

	"github.com/onsi/gomega/format"
)

type BeAnExistingFileMatcher struct {
	expected interface{}
}

func (matcher *BeAnExistingFileMatcher) Match(actual interface{}) (success bool, err error) {
	actualFilename, ok := actual.(string)
	if !ok {
		return false, fmt.Errorf("BeAnExistingFileMatcher matcher exp
    
func (matcher *BeAnExistingFileMatcher) Match(actual interface{}) (success bool, err error) {
	actualFilename, ok := actual.(string)
	if !ok {
		return false, fmt.Errorf("BeAnExistingFileMatcher matcher expects a file path")
	}

	if _, err = os.Stat(actualFilename); err != nil {
		switch {
		case os.IsNotExist(err):
			return false, nil
		default:
			return false, err
		}
	}

	return true, nil
}