deep copy lua table

deepcopy.lua

-- deepcopy a lua table, no recursion sub table, the key never be a table.

local function _copy(obj, target)
	local n = 0
  -- clear target table
	for k,v in pairs(target) do
		if type(v) == "table" then
			v.__del = true
			n = n + 1
		else
			target[k] = nil
		end
	end
  -- copy obj into target
	for k,v in pairs(obj) do
		if type(v) == "table" then
			local t = target[k]
			if t then
				t.__del = nil
				n = n - 1
			else
				t = {}
				target[k] = t
			end
			_copy(v, t)
		else
			target[k] = v
		end
	end
  -- clear no use sub table in target
	if n > 0 then
		for k,v in pairs(target) do
			if type(v) == "table" and v.__del then
				target[k] = nil
			end
		end
	end
end

local function deepcopy(obj, target)
	target = target or {}
	_copy(obj, target)
	return target
end

------ test ---------

local print_r = require "print_r"

a = { a=1, b=2 , c = {} }

print_r(a)

local b = deepcopy(a, { d = 3, c = { a = 1} } )

print "---------------------------"

print_r(b)