Memory management
Qt organizes the Qt objects hierarchically. An object can be an orphan or can be the child of another object. When a Qt object is deleted, all its descendants are deleted as well. When programming in C++, orphan objects must be deleted manually.
Two situations arise when a Qt object is exposed the Lua interpreter.
- An exposed Qt object may be deleted by C++ code,
either directly, or indirectly because one of its
ascendant has been deleted.
The Lua userdata representing the object becomes a "zombie".
Zombies can be detected using method
tobool().
- An exposed Qt object may be deleted because the Lua garbage collector determines that the Lua program no longer needs this object. Whether this happens is determined when the object is exposed to the Lua interpreter. Such objects are said to be owned by Lua.
In general, orphan objects created from a Lua program are owned by Lua. Objects with a parent and orphan objects created from C++ code are not Lua owned and are not affected by the decisions of the Lua garbage collector.