how to find out all properties of an object in lua?

Question

Is there any way of getting all the non-nil parameters / properties of an object? I found this: getmetadata(self.xxxx) and i am looking for something like: ge

Answer 1

I'm going to assume that when you are referring to "objects" you are meaning "lua tables with an __index metatable pointing to other tables". If that is not the case, this answer will not help you.

If your object structure is made with tables (this is, all __indexes are tables) then you can "parse them up" to obtain all the properties and inherited properties.

If you have any function as __index then what you ask is impossible; there's no way to get the "list of values for which a function returns a non-nil value".

In the first case, the code would look like this:

function getAllData(t, prevData)
  -- if prevData == nil, start empty, otherwise start with prevData
  local data = prevData or {}

  -- copy all the attributes from t
  for k,v in pairs(t) do
    data[k] = data[k] or v
  end

  -- get t's metatable, or exit if not existing
  local mt = getmetatable(t)
  if type(mt)~='table' then return data end

  -- get the __index from mt, or exit if not table
  local index = mt.__index
  if type(index)~='table' then return data end

  -- include the data from index into data, recursively, and return
  return getAllData(index, data)
end

But remember, if any of your __indexes is a function, there is no way to get all the properties; at least not from Lua.