You've always wanted method_missing in lua, right? This is a pretty close approximation.

method_missing.lua

--[[
Method missing should be an optional definition on any object.
If a method cannot be found, method_missing is called if available
]]

local field = '__method__missing'

function method_missing(selfs, func)
    
    local meta = getmetatable(selfs)
    local f
    if meta then
        f = meta.__index
    else
        meta = {}
        f = rawget
    end
    meta.__index = function(self, name)
        local v = f(self, name)
        if v then
            return v
        end
        
        rawget(self, name)[field] = function(...)
            return func(self, name, ...)
        end
    end
    
    setmetatable(selfs, meta)
end

debug.setmetatable(nil, { __call = function(self, ...) 
    if self[field] then
        return self[field](...)
    end
    return nil
end, __index = function(self, name) 
    if name~=field then error("attempt to index a nil value") end
    return getmetatable(self)[field]
end, __newindex = function(self, name, value)
    if name~=field then error("attempt to index a nil value") end
    getmetatable(self)[field] = value
end} )

return method_missing