How to detect if a non-beacon machine can accept modules

[AlexTheNotsogreat]

I'm trying to implement a way for machines to disable if there's too many beacons surrounding it, but the following function isnt working.

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script.on_event(defines.events.on_built_entity, function(event)
local machine = event.created_entity
  if machine.prototype.allowed_effects == true then
    if beacons_count > 1 then
      machine.active = false
    end
  end
end)

the problem itself is the machine.prototype.allowed_effects conditional; since it refers to the entity prototype it doesnt result in an error, but it also seems to never be true regardless of whether or not a machine actually does accept module or beacon effects. Removing that condition and just using the beacons_count conditional works for entities that accept effects but gives an error message otherwise, meaning I can't bypass it.

[Pi-C]

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  if machine.prototype.allowed_effects == true then
	…
  end

the problem itself is the machine.prototype.allowed_effects conditional; since it refers to the entity prototype it doesnt result in an error,

Sorry, you're wrong! The condition doesn't result in an error because it's refers to an entity prototype!

but it also seems to never be true regardless of whether or not a machine actually does accept module or beacon effects.

Your base assumption is wrong:

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type(machine.prototype.allowed_effects) == "boolean"

You can check that for yourself, just add this line before the condition check:

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game.print("machine.prototype.allowed_effects: "..serpent.block(machine.prototype.allowed_effects))

If you check the description of LuaEntityPrototype::allowed_effects, you'll find that its value is a dictionary mapping strings to a boolean. Even if the entity prototype doesn't allow for beaconed effects, machine.prototype.allowed_effects will not be 'false', but an empty table. So what you really want to know is whether that table is empty! You could check for

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table_size(machine.prototype.allowed_effects) > 0

or simply use

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if next(machine.prototype.allowed_effects) then … end