Memoize by Joe Albahari https://t.co/TvXLvFqoOR

memoize.cs

void Main()
{

	Expensive(100).Dump(); // takes 2 secs
	Expensive(100).Dump(); // immediate
	
	ExpensiveOther(100).Dump(); // takes 2 secs
	ExpensiveOther(100).Dump(); // immediate	
}

static int SomeNsExpensive(int x) {Thread.Sleep(2000);return x*10;}

readonly Func<int, int>
	Expensive = Memoize<int,int>(SomeNsExpensive);

readonly Func<int, int>
	ExpensiveOther = Memoize<int,int>(SomeNsExpensive);


static Func<TIn, TOut> Memoize<TIn,TOut> (Func<TIn, TOut> func) {

	var cache = new Dictionary<TIn, TOut>();
	return (input => {
	
		TOut result;
		if (cache.TryGetValue (input, out result)) return result;
		return cache[input] = func(input);
	
	});

}