assignment doesn't modify the variable in List ForEach function with lambda expression

I'm writing a simpl开发者_StackOverflow中文版e encrypting for my homework. I have completed it, now i'm trying to improve my code with lambda expressions. Object in list doesn't change after lambda expression. Is it using a local variable ? And how can i do that with lambda expression. I wrote my code following

public override string Encrypt(string code)
    {
        List<Byte> encodedBytes = new List<Byte>(ASCIIEncoding.ASCII.GetBytes(code));

        encodedBytes.ForEach(o => { if (hash.Contains(o)) 
            o = hash.ElementAt((hash.IndexOf(o) + ShiftAmount) % hash.Count); });            

        return ASCIIEncoding.ASCII.GetString(encodedBytes.ToArray());                
    }

I'm waiting for your answer, thanks...

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It is indeed using a local variable. If you want the return value of the lambda to assign back into the list, use ConvertAll instead of ForEach.

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If you want a more problem related solution this will be more suitable

public static class Extensions
{
    public static void ModifyWhere<T>(this List<T> list, Func<T, bool> condition, Func<T, T> act)
    {
        for (int i = 0; i < list.Count; i++)
        {
            if (condition(list[i]))
                list[i] = act(list[i]);
        }
    }
}

and this solution won't be specific, method taking a bool returning function as a condition, and returning function as an action.

a sample usage will be following

mylist.ModifyWhere(someBoolReturningFunction, someTReturningFunction);

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Yes, in your code the variable 'o' is a local variable in the scope of the anonymous method passed to the ForEach method. Changes to it will not be reflected outside that scope.

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You could write your own extension method to iterate over your list, modifying the items and then returning a new list based on your lambda like this:

public static class Extensions
{
  public static List<T> ModifyEach<T>(this List<T> list, Func<T, T> method)
  {
    List<T> mod = new List<T>();

    foreach (T e in list)
    {
      mod.Add(method(e));
    }

    return mod;
  }
}

Sample usage:

List<string> f = new List<string>()
{
  "hello",
  "world"
};

f = f.ModifyEach(x => x.ToUpper());
f.ForEach(x => Console.WriteLine(x));