func checkThing(state *lua.State, argNum int) *Thing {
userdata := state.CheckUdata(argNum, ThingMetaTableName)
if userdata == nil {
state.ArgError(argNum, "`Thing` expected")
}
var thingPtr *int64
thingPtr = (*int64)(userdata)
thingId := ThingId(*thingPtr)
thing := World.ThingForId(thingId)
if thing == nil {
state.ArgError(argNum, "`Thing` argument is no longer valid")
}
return thing
}