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 wrote my own printObject code.. here it is

function printObj(obj, hierarchyLevel) 
  if (hierarchyLevel == nil) then
    hierarchyLevel = 0
  elseif (hierarchyLevel == 4) then
    return 0
  end

  local whitespace = ""
  for i=0,hierarchyLevel,1 do
    whitespace = whitespace .. "-"
  end
  io.write(whitespace)

  print(obj)
  if (type(obj) == "table") then
    for k,v in pairs(obj) do
      io.write(whitespace .. "-")
      if (type(v) == "table") then
        printObj(v, hierarchyLevel+1)
      else
        print(v)
      end           
    end
  else
    print(obj)
  end
end

This is the opposite approach then the post before used. Go through all key value pairs in the table. If the value of one index is a table, go through this table. This solution will not get the upwards metatables like the other post did

Answer 2

I believe objects are just a table, so you should be able to iterate over the properties as any other table:

for i,v in ipairs(your_object) do body end

Answer 3

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.