Prevent other classes from altering a list in a class

Question

If I have a class that contains, for example, a List and I want other classes to be able to see the list but not set it, I can declare

Answer 1

You won't be able to use an autoproperty.

public class SomeClass()
{
    private List<string> someList;
    public IList<string> SomeList { 
        get { return someList.AsReadOnly(); }
    }
}

Answer 2

public class SomeClass()
{
    private List<string> _someList = new List<string>();

    public IList<string> SomeList 
    { 
         get { return _someList.AsReadOnly(); } 
    }
}

Answer 3

Return IEnumerable<string>, which is immutable. The getter should look like this:

public IEnumerable<string> SomeList
{
   get
   {
      foreach(string s in someList) yield return s; // excuse my inline style here, zealots
      yield break;
   }
}

Answer 4

You'll want to return the list as a ReadOnly list. You can do this with the following code:

using System.Collections.ObjectModel;

public ReadOnlyCollection<string> GetList() {
    return SomeList.AsReadOnly();
}