How do I change my new list without changing the original list?

Question

I have a list that gets filled in with some data from an operation and I am storing it in the memory cache. Now I want another list which contains some sub data from the li

Answer 1

Since a List is a reference type, what is passed to the function is a reference to the original list.

See this MSDN article for more information about how parameters are passed in C#.

In order to achieve what you want, you should create a copy of the list in SomeOperationFunction and return this instead. A simple example:

void List SomeOperationFunction(List target)
{
  var newList = new List(target);
  newList.RemoveAt(3);
  return newList; // return copy of list
}

As pointed out by Olivier Jacot-Descombes in the comments to another answer, it is important to bear in mind that

[...] the list still holds references to the same items if the items are of a reference type. So changes to the items themselves will still affect the items in both lists.