How to get __metatable function to be called?

Question

My goal

Get getmetatable to return the return value of the function assigned to the __metatable field.

Code:

local x, m = {}, {__metatable = function() return nil end};
setmetatable(x, m);
io.write("Let's get the metatable:", tostring(getmetatable(x)), "\n");

But I'm getting the actual function rather than return.

So how do I get it to be called so I can get nil? So it seems like it has no metatable?

You can redefine global function `getmetatable()` to change the logic if the argument equals to your `x` — Egor Skriptunoff, Sep 18 '19 at 16:24
You could approximate that behavior by setting `__metatable` to `false` — DarkWiiPlayer, Sep 19 '19 at 13:47
Hiding the existence of a metatable is futile if `setmetatable` is also available. — siffiejoe, Sep 20 '19 at 06:30

DarkWiiPlayer · Accepted Answer · 2019-09-20T06:05:30.807

Just rewrite getmetatable to work the way you want it to ;)

do local getmetatable = getmetatable
   function _G.getmetatable(tab)
      local meta = getmetatable(tab)
      if type(meta)=='function' then
         return meta(tab)
      else
         return meta
      end
   end
end

Alternatively, you could just set __metatable to false. This would work for code written like if getmetatable(foo) then, but would break to code like if getmetatable(foo) == false. Arguably, the first is the one you should use, but there's likely someone out there doing the second one.

That'd also hint to the user that there is a metatable, it's just none of their busyness to mess with it.

How to get __metatable function to be called?

My goal

1 Answers1