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PODisposing an IDisposable in Linq
 

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    <p><em>(This is a follow on from a comment on an answer to <a href="https://stackoverflow.com/questions/1751153/how-do-you-dispose-of-idisposableobject-create-inside-of-a-linq-expression">this</a> question)</em></p> <p>18 months after I posted it, someone spotted a bug in <a href="https://stackoverflow.com/questions/21280/am-i-missing-something-about-linq/80709#80709">one of my Linq examples</a>, where I use an IDisposable half way through a method chain, which never gets disposed.</p> <p>I attempted to write an extension method to handle this:</p> <pre><code>public static IEnumerable&lt;R&gt; Using&lt;T, R&gt;( this IEnumerable&lt;T&gt; list, Func&lt;T, R&gt; selector) where R : IDisposable { foreach(var item in list) using(var disposable = selector(item)) yield return disposable; } var q = Enumerable.Range(0, 10) .Using(i =&gt; new Disposable(i)) .Select(d =&gt; d.Id); </code></pre> <p>After seeing <a href="https://stackoverflow.com/questions/1751153/how-do-you-dispose-of-idisposableobject-create-inside-of-a-linq-expression/1751277#1751277">Marc's answer</a> to the question I referenced above, I wondered if I could overload the Select extension method directly, but if I do (by renaming <code>Using</code> to <code>Select</code>), the compiler squeals about <code>Select(d =&gt; d.Id)</code>, because <code>There is no implicit conversion from 'string' to 'System.IDisposable'</code>.</p> <p>Here's a test class...</p> <pre><code>public class Disposable : IDisposable { private string _id; private bool _disposed = false; public Disposable(int id) { Id = id.ToString(); Console.WriteLine("Creating " + Id); } public void Dispose() { Console.WriteLine("Disposing " + Id); _disposed = true; } public string Id { get { if(_disposed) throw new Exception("Call to disposed object!"); return _id; } set { _id = value; } } } </code></pre>
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