@cache in C++

memoize.cpp

#include<iostream>
#include<functional>
#include<map>
#include<tuple>
using namespace std;

// start class definition
template<class>
struct memoize{};

template<class R, class... Args>
struct memoize<R(Args...)>
{
	map<tuple<Args...>,R> db;
	function<R(Args...)> func;
	template<class T>
	memoize(T t):func(t){}
	R operator()(Args... Ar)
	{
		if(db.count({Ar...}))
		return db[{Ar...}];
		R res=func(Ar...);
		db[{Ar...}]=res;return res;
	}
};
// end class definition

memoize<long(int,int)> binom=
[](int n,int r)->long
{
	if(r==0||r==n)return 1;
	if(r==1||r==n-1)return n;
	return (binom(n-1,r-1)+binom(n-1,r));
};
// usage example