a heavily commented example of using metatables to implement class-like behaviour in lua

metatable_example.lua

--define the example class table
local example_class = {}

--build the class metatable
--this is instructions to lua for what we want instances to do in certain circumstances
example_class.mt = {
	--we only really care about the index metamethod
	--this one says that if something is missing in the table this metatable is set on
	--to go look in the example_class table
	__index = example_class,
}

--build an instance of the example class
function example_class:new()
	--build the instance table
	--we can include any instance member variables here
	--which will be defined per-instance
	--rather than per-class
	local instance = {
		member_variable = "whatever you want",
	}
	--set the metatable on the instance to the one we defined earlier
	setmetatable(instance, self.mt)
	--return it
	return instance
end

--define some method to use
function example_class:some_method()
	print("fantastic!", self.member_variable)
end

--lets create some instances
local a = example_class:new()
local b = example_class:new()
--we'll modify one of them, to show that the data isn't shared
b.member_variable = "changed to something new"

--lets see what they print out when we call the method on each instance
a:some_method() --prints "fantastic		whatever you want"
b:some_method() --prints "fantastic		changed to something new"