ReadOnlyCollection or IEnumerable for exposing member collections?

Posted by Erik Öjebo on Stack Overflow See other posts from Stack Overflow or by Erik Öjebo
Published on 2009-01-29T12:20:04Z Indexed on 2010/06/10 5:42 UTC
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Is there any reason to expose an internal collection as a ReadOnlyCollection rather than an IEnumerable if the calling code only iterates over the collection?

class Bar
{
    private ICollection<Foo> foos;

    // Which one is to be preferred?
    public IEnumerable<Foo> Foos { ... }
    public ReadOnlyCollection<Foo> Foos { ... }
}


// Calling code:

foreach (var f in bar.Foos)
    DoSomething(f);

As I see it IEnumerable is a subset of the interface of ReadOnlyCollection and it does not allow the user to modify the collection. So if the IEnumberable interface is enough then that is the one to use. Is that a proper way of reasoning about it or am I missing something?

Thanks /Erik

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