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: have_existing_field_matcher.go
    path of file: ./repos/hoverfly/vendor/github.com/onsi/gomega/matchers
    
    the code of the file until where you have to start completion: package matchers

import (
	"errors"
	"fmt"

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

type HaveExistingFieldMatcher struct {
	Field string
}

func (matcher *HaveExistingField
    
func (matcher *HaveExistingFieldMatcher) Match(actual interface{}) (success bool, err error) {
	// we don't care about the field's actual value, just about any error in
	// trying to find the field (or method).
	_, err = extractField(actual, matcher.Field, "HaveExistingField")
	if err == nil {
		return true, nil
	}
	var mferr missingFieldError
	if errors.As(err, &mferr) {
		// missing field errors aren't errors in this context, but instead
		// unsuccessful matches.
		return false, nil
	}
	return false, err
}