Q_NAMESPACE across multiple files

Creaperdown

Hey, I have a folder called common/enums in which I want to store some enums which I also want to register to QML. I am using Q_NAMESPACE combined with Q_ENUM_NS to do this. This works just fine for one enum, but when adding another, I am getting this error:

In file included from /home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/mocs_compilation.cpp:3:
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_common_mocked_namespace.cpp:24:8: error: redefinition of ‘struct qt_meta_stringdata_application_t’
24 | struct qt_meta_stringdata_application_t {
|        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/mocs_compilation.cpp:2:
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:24:8: note: previous definition of ‘struct qt_meta_stringdata_application_t’
24 | struct qt_meta_stringdata_application_t {
|        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_common_mocked_namespace.cpp:33:47: error: redefinition of ‘const qt_meta_stringdata_application_t qt_meta_stringdata_application’
33 | static const qt_meta_stringdata_application_t qt_meta_stringdata_application = {
|                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:33:47: note: ‘const qt_meta_stringdata_application_t qt_meta_stringdata_application’ previously defined here
33 | static const qt_meta_stringdata_application_t qt_meta_stringdata_application = {
|                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_common_mocked_namespace.cpp:42:19: error: redefinition of ‘const uint qt_meta_data_application []’
42 | static const uint qt_meta_data_application[] = {
|                   ^~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:53:19: note: ‘const uint qt_meta_data_application [34]’ previously defined here
53 | static const uint qt_meta_data_application[] = {
|                   ^~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_common_mocked_namespace.cpp:58:38: error: redefinition of ‘const QMetaObject application::staticMetaObject’
58 | QT_INIT_METAOBJECT const QMetaObject application::staticMetaObject = { {
|                                      ^~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:81:38: note: ‘const QMetaObject application::staticMetaObject’ previously defined here
81 | QT_INIT_METAOBJECT const QMetaObject application::staticMetaObject = { {
|                                      ^~~~~~~~~~~
In file included from /home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/mocs_compilation.cpp:4:
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_settings_keys.cpp:24:8: error: redefinition of ‘struct qt_meta_stringdata_application_t’
24 | struct qt_meta_stringdata_application_t {
|        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:24:8: note: previous definition of ‘struct qt_meta_stringdata_application_t’
24 | struct qt_meta_stringdata_application_t {
|        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_settings_keys.cpp:33:47: error: redefinition of ‘const qt_meta_stringdata_application_t qt_meta_stringdata_application’
33 | static const qt_meta_stringdata_application_t qt_meta_stringdata_application = {
|                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:33:47: note: ‘const qt_meta_stringdata_application_t qt_meta_stringdata_application’ previously defined here
33 | static const qt_meta_stringdata_application_t qt_meta_stringdata_application = {
|                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_settings_keys.cpp:57:19: error: redefinition of ‘const uint qt_meta_data_application []’
57 | static const uint qt_meta_data_application[] = {
|                   ^~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:53:19: note: ‘const uint qt_meta_data_application [34]’ previously defined here
53 | static const uint qt_meta_data_application[] = {
|                   ^~~~~~~~~~~~~~~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_settings_keys.cpp:88:38: error: redefinition of ‘const QMetaObject application::staticMetaObject’
88 | QT_INIT_METAOBJECT const QMetaObject application::staticMetaObject = { {
|                                      ^~~~~~~~~~~
/home/creapermann/Programming/Etovex/Librum/build-Debug/src/application/application_autogen/QVJXAE3BGF/moc_book_operation_status.cpp:81:38: note: ‘const QMetaObject application::staticMetaObject’ previously defined here
81 | QT_INIT_METAOBJECT const QMetaObject application::staticMetaObject = { {
|                                      ^~~~~~~~~~~
[35/87] Building CXX object src/application/core/gene...ularGenerator_comicbook.dir/generator_comicbook.cpp.o
ninja: build stopped: subcommand failed.

I known that this is a known bug (or problem), since there are multiple bug reports for it (https://bugreports.qt.io/browse/QTBUG-68611).
Non the less, is there a work around so that one is able to have enums in the same namespace registered to QML?
My classes both look like this (Just with a different enum name):

namespace application
{

Q_NAMESPACE

enum class BookOperationStatus
{
    Success,
    OpeningBookFailed,
    BookDoesNotExist,
    PropertyDoesNotExist,
    TagDoesNotExist,
    TagAlreadyExists,
    OperationFailed
};

Q_ENUM_NS(BookOperationStatus)

}  // namespace application

Thanks in advance

ChrisW67

@Creaperdown said in Q_NAMESPACE across multiple files:

Non the less, is there a work around so that one is able to have enums in the same namespace registered to QML?

Perhaps this will work for you.
Group all the QObject-related declarations into a single header and put nothing QObject related in the others. Use a little macro magic to get all the enum declarations inside a single namespace { } block to work around moc not having a full C++ parser.

#ifndef ENUMDECL_H
#define ENUMDECL_H

#include <QObject>

namespace application
{

#include "enum1.h"
#include "enum2.h"

Q_NAMESPACE
Q_ENUM_NS(Enum1)
Q_ENUM_NS(Enum2)

}

#endif // ENUMDECL_H

#ifndef ENUM1_H
#define ENUM1_H

#ifndef ENUMDECL_H
namespace application
{
#endif

enum class Enum1
{
    Enum1_Value1,
    Enum1_Value2,
    Enum1_Value3
};

#ifndef ENUMDECL_H
}  // namespace application
#endif

#endif // ENUM1_H

#ifndef ENUM2_H
#define ENUM2_H

#ifndef ENUMDECL_H
namespace application
{
#endif

enum class Enum2
{
    Enum2_Value1,
    Enum2_Value2,
    Enum2_Value3
};

#ifndef ENUMDECL_H
}  // namespace application
#endif

#endif // ENUM2_H

HEADERS += \
    enumdecl.h

You will get just the one moc-related bunch of static structures in your code.

Edit: Not exactly sure how it will go with CMake

Creaperdown

This post is deleted!

Creaperdown

@ChrisW67 Thanks, this fixes it. Do you think there might be a way without the macro magic here though?

Creaperdown

A solution I came up with, is putting every enum into its own unique namespace to avoid the MOC duplication problems:

#pragma once
#include <QObject>

// Each enum needs to be in a separate namespace due to a Qt bug reported at:
// https://bugreports.qt.io/browse/QTBUG-81792
//
// This causes not being able to register multiple enums to the Qt type system
// and to QML (Q_NAMESPACE and Q_ENUM_NS), if they are in the same namespace.
// The work around is to create a separate namespace for each enum.
namespace application::setting_keys
{

Q_NAMESPACE

enum class SettingKeys
{
    Theme,
    PageSpacing,
    DisplayBookTitleInTitlebar,
    LayoutDirection,
    DisplayMode,
    PageTransition,
    DefaultZoom,
    SmoothScrolling,
    LoopAfterLastPage,
    CursorMode
};

Q_ENUM_NS(SettingKeys)

}  // namespace application::setting_keys

// Because the enum shouldn't be in a separate namespace in the first place,
// make the namespace available to all of its users to avoid syntactic clutter.
using namespace application::setting_keys;

If anyone finds a better solution, please let me know.