Question

What I want to do is this:

object.foo = "bar"

print(object.foo)

where “object” is a userdata.

I’ve been googling for a while (using the keyword __newindex and lua_rawset) but I can’t any examples that do what I want it to do.

I want to do this in with the lua api in c++

Answer 1

Let us write this in Lua code so that we can make quick experiments with the code

function create_object()
  -- ## Create new userdatum with a metatable
  local obj = newproxy(true)
  local store = {}
  getmetatable(obj).__index = store
  getmetatable(obj).__newindex = store
  return obj
end

ud = create_object()
ud.a = 10
print(ud.a)
-- prints '10'

If you work with userdata you probably want to do the above using the C API. However the Lua code should make it clear extactly which steps are necessary. (The newproxy(..) function simply creates a dummy userdata from Lua.)