Lua class lib with 'base' helper method

class.lua

-- test.lua
-- using the class lib and the introspective base helper method

class 'A'
function A:test()
	print "Hi"
end

class 'B' (A)
function B:test()
	base() -- self.base.test( self ) would actually cause a stack overflow when calling C:test()
	print "Hello"
end

class 'C' (B)

C:test()
-- prints
--   Hi
--   Hello


-- test2.lua
-- much more performant alternative to get similar 'base' sugar

class 'B2' (A)
local base = B2.test -- 'B2' here so if subclass gets modified in line above, this doesn't need to be updated
function B2:test()
	base( self )
	print "Hello"
end

class 'C2' (B2)

C2:test()
-- prints
--   Hi
--   Hello


-- class.lua

local function isa( self, name )	
	repeat 
		if self.__name == name then
			return true
		end
		self = self.__base
	until not self	
	return false
end

function class ( name )
	local class = { 
		__name = name; 
		isa = isa;
	}	
	local instance_mt = { __index = class; }
	class.new = function(...)
		local instance = setmetatable( {}, instance_mt )
		instance:init( ... )
		return instance
	end	
		
	getfenv( 2 )[ name ] = class
	return 
		setmetatable( {}, {			
			__call = function(t,superclass)		
				class.__base = superclass
				setmetatable( class, {__index = superclass } )
			end
		} )
end


local getinfo,getlocal,rawget = debug.getinfo, debug.getlocal, rawget -- make local for speed
function base( ... )
	local methodname,caller,self
	do -- inspect stack to find caller and self
		local callerinfo = getinfo(2, "nf")		
		local localname, localval = getlocal(2, 1)		
		assert( callerinfo.namewhat == "method" and localname == "self" and localval )	
		methodname = callerinfo.name
		caller = callerinfo.func
		self = localval
	end
	
	local nextbase,basecall -- loop vals
	nextbase = self
	repeat -- find the function that called base
		basecall = rawget( nextbase, methodname ) 
		if basecall == caller then			
			break
		end
		nextbase = nextbase.__base
	until not nextbase
	
	nextbase = nextbase.__base
	while nextbase do -- call the next one up the inheritence tree
		basecall = rawget( nextbase, methodname )
		if basecall ~= caller then
			return basecall( self, ... )
		end
		nextbase = nextbase.__base
	end
	
	error( "base() called by non-overrided method" )
end