table and userdata pattern (attributes on userdata)

[Gaspard Bucher <gaspard@...>]

Hi list !

I have C++ classes that I would like to extend in Lua (for example a FileObserver class that should store the observed files in Lua). Until now, I have been using composition:

==== SOLUTION A

instance = { super = mimas.FileObserver() }

function instance.super.pathChanged(path)

  instance:pathChanged(path)

end

--- But this is not great because I have to define C++ to Lua accessors like this (since "self" is not the same).

==== SOLUTION B

instance = mimas.FileObserver()

-- set any attribute (I could manage this with __newindex, __index in C++ but it seems slow).

instance.watched_files = {}

function instance:pathChanged(path)

  -- self == instance

  -- I can access watched_files

end

=====

The cleanest solution is "B", but there is a pretty big overhead on each member access (Lua --> mimas.FileObserver meta table --> C++ binding --> __index --> userdata env table). Is there another solution ?

Thanks for any hints,

Gaspard