signature/policy_config.go
func newPRMExactReference(dockerReference string) (*prmExactReference, error) {
	ref, err := reference.ParseNormalizedNamed(dockerReference)
	if err != nil {
		return nil, InvalidPolicyFormatError(fmt.Sprintf("Invalid format of dockerReference %s: %s", dockerReference, err.Error()))
	}
	if reference.IsNameOnly(ref) {
		return nil, InvalidPolicyFormatError(fmt.Sprintf("dockerReference %s contains neither a tag nor digest", dockerReference))
	}
	return &prmExactReference{
		prmCommon:       prmCommon{Type: prmTypeExactReference},
		DockerReference: dockerReference,
	}, nil
}
func newPRMExactReference(dockerReference string) (*prmExactReference, error) {
	ref, err := reference.ParseNormalizedNamed(dockerReference)
	if err != nil {
		return nil, InvalidPolicyFormatError(fmt.Sprintf("Invalid format of dockerReference %s: %s", dockerReference, err.Error()))
	}
	if reference.IsNameOnly(ref) {
		return nil, InvalidPolicyFormatError(fmt.Sprintf("dockerReference %s contains neither a tag nor digest", dockerReference))
	}
	return &prmExactReference{
		prmCommon:       prmCommon{Type: prmTypeExactReference},
		DockerReference: dockerReference,
	}, nil
}
// newPRMExactReference is NewPRMExactReference, except it resturns the private type.