type missingFieldError … func (e missingFieldError) Error() string { … } func extractField(actual interface{ … } type HaveFieldMatcher … func (matcher *HaveFieldMatcher) expectedMatcher() omegaMatcher { … } func (matcher *HaveFieldMatcher) Match(actual interface{ … } func (matcher *HaveFieldMatcher) FailureMessage(actual interface{ … } func (matcher *HaveFieldMatcher) NegatedFailureMessage(actual interface{ … }