Function MutableExtension

depends/protobuf/google/protobuf/extension_set.h:833–837

            ::google::protobuf::internal::FieldType field_type,                         \
            bool is_packed>                                                   \
  inline typename _proto_TypeTraits::MutableType MutableExtension(            \
      const ::google::protobuf::internal::ExtensionIdentifier<                          \
        CLASSNAME, _proto_TypeTraits, field_type, is_packed>& id) {           \
    return _proto_TypeTraits::Mutable(id.number(), field_type, &_extensions_);\
  }                                                                           \
                                                                              \
  template <typename _proto_TypeTraits,                                       \
            ::google::protobuf::internal::FieldType field_type,                         \