Retrieving lambda expressions from a collection

Question

I'm very new to lambda expressions in C#, and I'm having trouble conceptualizing how they are stored/retrieved in a collection.

I'm trying to programatically create a list of 10 Funcs x => x + 1, x => x + 2, etc. as a test. My desired output is 0,1,2,3,4,5,6,7,8,9

Here is my code for that:

 var list = new List<Func<int, int>>();
 for (int i = 0; i < 10; i++)
 {     
   Func<int, int> func = x => x + i;
   Console.WriteLine("a) " + func.Invoke(0)); //returns 0,1,2,3,4,5,6,7,8,9

   list.Add(func);
   Console.WriteLine("b) " + list[i].Invoke(0)); //returns 0,1,2,3,4,5,6,7,8,9
 }

 foreach (var func in list) //returns 10,10,10,10,10,10,10,10,10,10
   Console.WriteLine("c) " + func.Invoke(0)); 

 for(int i = 0; i < list.Count; i++) //returns 10,10,10,10,10,10,10,10,10,10
    Console.WriteLine("d) " + list[i].Invoke(0)); 

I get the same results when substituting a Func array for the List[Func].

What am I missing?

Answer 1

Make i local to the lambda by copying it into a new variable:

var list = new List<Func<int, int>>();
for (int i = 0; i < 10; i++)
{
    var temp = i;
    Func<int, int> func = x => x + temp;
    Console.WriteLine("a) " + func.Invoke(0)); //returns 0,1,2,3,4,5,6,7,8,9

    list.Add(func);
    Console.WriteLine("b) " + list[i].Invoke(0)); //returns 0,1,2,3,4,5,6,7,8,9
}

foreach (var func in list) //returns 0,1,2,3,4,5,6,7,8,9
    Console.WriteLine("c) " + func.Invoke(0));

for (int i = 0; i < list.Count; i++) //returns 0,1,2,3,4,5,6,7,8,9
    Console.WriteLine("d) " + list[i].Invoke(0));