Question

I have an API that returns XElement‘s, and I want the document behind those XElement‘s to be immutable (read-only). I need it for:

• Not to give devs an ability to change it accidentally 🙂
• Improving performance – creating a copy of an XDocument might be a performance “heavy” operation in some cases.

It doesn’t seem to possible to inherit & override the necessary behavior in XDocument/XElement/XContainer, because all virtual methods there are marked as internal:

internal virtual void XContainer.AddAttribute(XAttribute a)
{
}

So my question is – is there a way make it happen, or it is better to have a different API that will either return something like XPathNavigator‘s, or it is better to have own classes like IReadOnlyXElement, etc.?

Answer 1

You could create an XElement wrapper that is similar to ReadOnlyCollection<T>.

public sealed class ReadOnlyXElement
{
    private readonly XElement _element;


    public string Value
    {
        get { return _element.Value; }
    }


    public ReadOnlyXElement(XElement element)
    {
        _element = element;
    }


    public IEnumerable<ReadOnlyXElement> Elements()
    {
        foreach (var child in _element.Elements())
        {
            yield return new ReadOnlyXElement(child);
        }
    }

    public IEnumerable<ReadOnlyXElement> Elements(XName xname)
    {
        foreach (var child in _element.Elements(xname))
        {
            yield return new ReadOnlyXElement(child);
        }
    }
}