Properly exposing a List?

Question

I know I shouldn\'t be exposing a List in a property, but I wonder what the proper way to do it is? For example, doing this:

public static          


        

Answer 1

Exposing a List as a property isn't actually the root of all evil; especially if it allows expected usage such as foo.Items.Add(...).

You could write a cast-safe alternative to AsEnumerable():

public static IEnumerable AsSafeEnumerable(this IEnumerable data) {
    foreach(T item in data) yield return item;
}

But your biggest problem at the moment is thread safety. As a static member, you might have big problems here, especially if it is in something like ASP.NET. Even ReadOnlyCollection over an existing list would suffer from this:

        List ints = new List { 1, 2, 3 };
        var ro = ints.AsReadOnly();
        Console.WriteLine(ro.Count); // 3
        ints.Add(4);
        Console.WriteLine(ro.Count); // 4

So simply wrapping with AsReadOnly is not enough to make your object thread-safe; it merely protects against the consumer adding data (but they could still be enumerating it while your other thread adds data, unless you synchronize or make copies).