Memoize example

1.cs

using System;
using System.Collections.Concurrent;
using System.Diagnostics;

public static class Program
{
    public static Func<T, V> MemoizeExt<T, V>(this Func<T, V> f) => a =>
        new ConcurrentDictionary<T, V>().GetOrAdd(a, f);

    public static Func<T, V> Memoize<T, V>(Func<T, V> f) => a =>
        new ConcurrentDictionary<T, V>().GetOrAdd(a, f);

    public static int DoIt(string a) => a.Length;
    

    static void Main()
    {
        Console.WriteLine(DoIt("aaaabba"));
        Console.WriteLine(DoIt("bbb"));

        // extension method: does not compile
        //var cachedDoit = DoIt.MemoizeExt();

        // static method: does not compile either
        // isn't DoIt() signature compatible with Func<string, int> ?
        //var cachedDoit = Memoize(DoIt);

        // static with explicit generic types: it works!
        // DoIt() signature IS compatible with Func<string, int>, but we have to specify types
        // but it is ugly, what if there's 3, 4 or more parameters
        var cachedDoit = Memoize<string, int>(DoIt);

        Console.WriteLine(cachedDoit("aaaabba"));
        Console.WriteLine(cachedDoit("bbb"));

        Console.Read();
    }
}