View difference between Paste ID: XtiZGY9X and kdSKLsSi

 class Program
     {
         // Can't do IDictionary<int, Func<T, String>> as T is not available here.
         private static readonly IDictionary<int, Object> _cache = new Dictionary<int, Object>();
 
         public static void SomeToStringCalls()
         {
             Console.WriteLine(ToString(i => (i + 1).ToString(), 1));
             Console.WriteLine(ToString(i => (i + 1).ToString(), 2));
             Console.WriteLine(ToString(i => (i + 2).ToString(), 3));
             Console.WriteLine(ToString(i => (i + 2).ToString(), 4));
         }
 
         private static int GetExpressionHash<T>(Expression<Func<T, string>> expression)
         {
             int hash = expression.Body.ToString().GetHashCode();
             // if you consider parameter unimportant - comment this line
             // using quite simple and error-prone hash function h = h * 31 + update
             // you might want to switch to md5 or sha in production
             expression.Parameters.ToList().ForEach(param => hash = hash * 31 + param.Name.GetHashCode());
             return hash;
         }
 
         private static string ToString<T>(Expression<Func<T, string>> expression, T input)
         {
             var cacheKey = GetExpressionHash(expression);
             if (!_cache.ContainsKey(cacheKey))
             {
                 _cache[cacheKey] = expression.Compile();
                 Console.WriteLine(String.Format("Compiling expression {0}", expression.ToString()));
             }
             var method = (Func<T, string>) _cache[cacheKey];
             return method.Invoke(input);
         }
 
         static void Main(string[] args)
         {
             SomeToStringCalls();
             Console.ReadLine();
         }
     }