cache function result with key

cachefunc.lua

-- https://weibo.com/2050899237/OpPODpfBK

local function cache_func(func, cap)
	cap = cap or 128
	local current_cache = {}
	local cache_meta = { __index = current_cache }
	local func_meta = { __index = nil }
	local prev_meta = { __index = nil }
	local n = 0
	
	local function renew_cache()
		prev_meta.__index = setmetatable(current_cache, func_meta)
		current_cache = setmetatable({}, prev_meta)
		cache_meta.__index = current_cache
	end
	
	renew_cache()
	
	function func_meta:__index(key)
		n = n + 1
		if n > cap then
			renew_cache()
			n = 0
		end
		local v = func(key)
		current_cache[key] = v
		return v
	end
	return setmetatable({}, cache_meta)
end

--- test

local cache = cache_func(function(key)
	return "key:" .. tostring(key)
end)

for i = 1, 256 do
	print(cache[i])
end