c# - Best practice: How to expose a read-only ICollection

Question

I have an ICollection<T> called foos in my class which I want to expose as read-only (see this question). I see that the interface defines a property .IsReadOnly, which seems appropriate... My question is this: how do I make it obvious to the consumer of the class that foos is read-only?

I don't want to rely on them remembering to query .IsReadOnly before trying a not-implemented method such as .Add(). Ideally, I would like to expose foos as a ReadOnlyCollection<T>, but it does not implement IList<T>. Should I expose foo via a method called, for example, GetReadOnlyFooCollection rather than via a property? If so, would this not confuse someone who then expects a ReadOnlyCollection<T>?

This is C# 2.0, so extension methods like ToList() are not available...

Answer 1

You can make "foos" a ReadOnlyCollection like this:

ReadOnlyCollection<T> readOnlyCollection = foos.ToList<T>().AsReadOnly();

Then you can expose it as a property of your class.

EDIT:

    class FooContainer
    {
        private ICollection<Foo> foos;
        public ReadOnlyCollection<Foo> ReadOnlyFoos { get { return foos.ToList<Foo>().AsReadOnly();} }

    }

Note: You should remember that once you get the ReadOnlyFoos collection is no longer "synchronized" with your foos ICollection. See the thread you referenced.