setmetatable/getmetatable are invalid?

[+Hügh]

@fm34 and I spent some time debugging a cartridge of his. After a while, he narrowed it down to the usage of setmetatable and getmetatable in a table deepcopy function. I'm certain that I've seen setmetatable and getmetatable used before.

 

Why has it stopped working?

Edited March 24, 2021 by Hügh

[+Hügh]

For context, the following cartridge is "valid" and compiles correctly...

 

require "Wherigo"

ZonePoint = Wherigo.ZonePoint
Distance = Wherigo.Distance
Player = Wherigo.Player

_cartridge = Wherigo.ZCartridge()

_cartridge.Id = "00000000000000000000000000001337"
_cartridge.Name = "Sandbox"
_cartridge.Activity = "Geocache"
_cartridge.Version = ""
_cartridge.Company = ""
_cartridge.Author = "Hugh"
_cartridge.TargetDevice = "SmartPhone"
_cartridge.TargetDeviceVersion = "0"
_cartridge.BuilderVersion = "1"
_cartridge.StateId = "1"
_cartridge.CountryId = "2"
_cartridge.Description = [[A sandbox.]]
_cartridge.StartingLocationDescription = [[]]
_cartridge.Visible = true
_cartridge.Complete = false
_cartridge.UseLogging = false
_cartridge.CreateDate = "12/25/2020 04:02:56 AM"
_cartridge.PublishDate = "1/1/1970 01:00:00 AM"
_cartridge.UpdateDate = "12/25/2020 04:06:27 AM"
_cartridge.LastPlayedDate = "1/1/1970 01:00:00 AM"
_cartridge.StartingLocation = Wherigo.INVALID_ZONEPOINT

function f(_object)
    local _copy = {}

    return _copy
end

return _cartridge

 

But, the following do not.

 

require "Wherigo"

ZonePoint = Wherigo.ZonePoint
Distance = Wherigo.Distance
Player = Wherigo.Player

_cartridge = Wherigo.ZCartridge()

_cartridge.Id = "00000000000000000000000000001337"
-- SNIP
_cartridge.StartingLocation = Wherigo.INVALID_ZONEPOINT

function f(_object)
    local _copy = {}
    setmetatable(_copy, nil)

    return _copy
end

return _cartridge

 

require "Wherigo"

ZonePoint = Wherigo.ZonePoint
Distance = Wherigo.Distance
Player = Wherigo.Player

_cartridge = Wherigo.ZCartridge()

_cartridge.Id = "00000000000000000000000000001337"
-- SNIP
_cartridge.StartingLocation = Wherigo.INVALID_ZONEPOINT

function f(_object)
    local _copy = {}
    setmetatable(_copy, {})

    return _copy
end

return _cartridge