Hello everyone.

An application we are working on needs some parts to be scripted. The scripts will only act as callbacks to controle some part of the execution of some transactions. To do so, it must expose a few objects from the host application. The lifetime of these objects is well controled by the host and they will outlive the execution of the script. The logical choice seems to be the use of lightuser data.

We have exposed these objects using functions and lightuser data and it does work. However, lightuser data don't have their individual metatable. Instead, they all share the same so they all share the same metamethods. It would be great though if we could associate specific methods to each object exposed (like it can be done with full user data) so it would be possible to use object oriented programming notations on those objects from the script.

At the moment, we have to use a notation like this :

function f(user, logger)

   setName(user, "name")
   setGroup(user, "group")

   output(logger, "User is set.")

end

instead of

function f(user, logger)

   user:setName("name")
   user:setGroup("group")

   logger:output("User is set.")

end

Is there a way to do this with lightuser data ?

tbl.func(tbl, "parameter")

is the same as

tbl:func("parameter")

I don't know how this works on the C side, but in Lua, you'd declare and use a class like this:

local User = { };

function User.new()
    return setmetatable({ }, {__index = User});
end

function User:setName(name) -- Same as function User.setName(self, name)
    self.name = name
end


local user = User.new();
user:setName("John");

local user2 = User.new();
user2:setName("Jane");

print(user.name, user2.name); -- John, Jane

However I don't know if this helps you.

Is there a way to do this with lightuser data ?

http://bitsquid.blogspot.com.au/2011/06/lightweight-lua-bindings.html

Is there a way to do this with lightuser data ?

Pretty sure, no. I ended up using the syntax that apatriarca suggests. Here's another example of the same syntax being used due to the choice to use light userdata:

http://bitsquid.blogspot.com.au/2011/06/lightweight-lua-bindings.html

Thank you, i was pretty sure it wasn't possible, i asked just in case. The method suggested by apatriarca is what we are using, the functions are exposed via a call to luaL_newlib and lua_setglobal so they appear in a "namespace" or library.

I like to embed the light user data in a normal user data. Any functions called in the user data can then pull the light user data out in native code and work on it.

That's a very good idea. When i looked at it, i was thinking : why didn't i think about that . Thanks alot for sharing.