Re: Userdata Lifetime Management (was Prevent userdata from being marked for garbage collection?)

[Miles Bader <miles@...>]

Vinnie Falco <vinnie.falco@gmail.com> writes:
> - Lua lifetime: Managed completely by Lua
> - C++ lifetime: Managed completely by C++
> - Shared lifetime: Reference counted with your choice of compatible container.

I don't use LuaBridge, but I do similar stuff using SWIG.

One thing that I've found very handy is the ability to mark certain
functions/methods as _transferring_ an object from one "realm" to the
other.  This meshes well with C++ because the concept of object
ownership is pretty important in many C++ libraries.

For instance, a C++ method which returns an object pointer, which
should thereafter be managed by Lua (so the last reference in Lua to
that object should cause it to be deleted) is a C++ -> Lua transfer.
[Obviously the C++ code should not keep any references to the object
in this case]

Conversely, a C++ method which accepts an a pointer to a C++  object,
after which the Lua reference should become invalid, and the object is
now "owned" by the C++ side is an example of a Lua -> C++ transfer.

[For more complicated mixed usage, smart pointers of some sort are
useful, of course.]

-miles

-- 
Immortality, n.  A toy which people cry for, And on their knees apply for,
      Dispute, contend and lie for, And if allowed Would be right proud
      Eternally to die for.