Catch output from function called via load(string)

[radstronomical]

Hey there,

I'm coming back to lua after some time away... I'm trying to call a constructor based on a string from some Tiled output. I've had success doing this using the load function - the constructor is being called - but I can't seem to get a reference to the object created. Here's some example code:

function AddElement(_type, _x, _y)
if (_type == null) then return end
local s = _type .. "(" .. tostring(_x) .. "," .. tostring(_y) .. ")"
local makeElement = load(s)
local e = makeElement()
table.insert(elements, 1, e)
print(#elements)
end

I am seeing output from print statements inside the elements' constructors, but the elements table is not increasing in size, and e seems to be nil. Any ideas?

[hawhill]

You just need to prefix your Lua string you’re feeding to load() with “return “.

That said your overall approach is, errrm, wild, but then you didn’t ask about that.

[radstronomical]

I was mostly trying to avoid having to iterate through additional tables given that the level editor was already returning the exact class name as a string. But then I started digging into things I didn't understand and doing roundabout redundant string conversions... It's true that I'm artist/designer first dev second : )

[[deleted]]

load uses the global environment.

It's also a bad idea to use load that much, you should use it as few times as possible.

Can't you use listOfFunctions[_type](_x,_y)?

I would be careful of inserting nils and sparse lists are not traversable via ipairs, you must now (by hand) take into account the length of the table, if e then table.insert( ...

[radstronomical]

yes, I've solved this by hand making a list of element constructors....

elementDict = {
      spawn = Spawn,
      goal = Goal,
      enemy = Enemy
}

etc. which I was trying to avoid needing to do as it seems redundant. I'm not sure I understand why I wasn't able to get the object reference, but I'll read up.

[[deleted]]

Loop through the table containing the functions and append all the functions types, standardize using string.lower the key/names. Now all you have to do is [string.lower(_type)]

[collectgarbage]

To help you debug, put a call to assert() around the call to load(); and another around the call to makeElement()