Function Mutable

depends/protobuf/google/protobuf/extension_set.h:627–630

    set->SetString(number, field_type, value, NULL);
  }
  static inline string* Mutable(int number, FieldType field_type,
                                ExtensionSet* set) {
    return set->MutableString(number, field_type, NULL);
  }
};

class LIBPROTOBUF_EXPORT RepeatedStringTypeTraits {