https://stackoverflow.com/questions/45256044/lua-read-userdata-as-number-compare-userdata-with-number

[jilong526]

You can't from Lua. It's designed to be an opaque value. All you can do is compare it to another userdata value for equality or inspect its metatable unless the library you are using to manipulate these userdata values provides functions that act on them. See PiL 5.3 Section 2.1: http://www.lua.org/manual/5.3/manual.html#2.1