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POCastException attempting to call Action<KeyValuePair<>> delegate asynchronously
 

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    <p>I can't seem to figure out why I am getting an InvalidCastException running the following code:</p> <pre><code>var item = new KeyValuePair&lt;string, string&gt;("key", "value"); Action&lt;KeyValuePair&lt;string, string&gt;&gt; kvrAction = kvr =&gt;Console.WriteLine(kvr.Value); var result = kvrAction.BeginInvoke(item, null, null); kvrAction.EndInvoke(result); </code></pre> <p>Exception Info:</p> <pre><code>Test method Utilities.Tests.IEnumerableExtensionTests.ProveDelegateAsyncInvokeFailsForKeyValuePair threw exception: System.Runtime.Remoting.RemotingException: The argument type '[key, value]' cannot be converted into parameter type 'System.Collections.Generic.KeyValuePair`2[System.String,System.String]'. ---&gt; System.InvalidCastException: Object must implement IConvertible.. </code></pre> <p>Any assistance would be appreciated =) This code seems to work with anything I throw at it except a KeyValuePair&lt;>.</p> <p>Update: It appears this condition exists for any struct. I hadn't noticed KeyValuePair&lt;> was a struct and so was only testing with classes. I still don't understand why this is the case though. </p> <p>Update 2: Simon's answer helped confirm this behavior is unexpected, however implementing a custom type won't work for what I'm trying to do. I am trying to implement an extension method on IEnumerable&lt;> to execute a delegate Asynchronously for each item. I noticed the error running tests against a generic Dictionary object.</p> <pre><code> public static IEnumerable&lt;T&gt; ForEachAsync&lt;T&gt;(this IEnumerable&lt;T&gt; input, Action&lt;T&gt; act) { foreach (var item in input) { act.BeginInvoke(item, new AsyncCallback(EndAsyncCall&lt;T&gt;), null); } return input; } private static void EndAsyncCall&lt;T&gt;(IAsyncResult result) { AsyncResult r = (AsyncResult)result; if (!r.EndInvokeCalled) { var d = (Action&lt;T&gt;)((r).AsyncDelegate); d.EndInvoke(result); } } </code></pre> <p>I would rather not limit the method with a constraint on T to ensure only classes are used so I have refactored the method as follows to get around the problem with BeginInvoke but I have not worked with the TreadPool directly before and would like to make sure I am not missing anything important.</p> <pre><code> public static IEnumerable&lt;T&gt; ForEachAsync&lt;T&gt;(this IEnumerable&lt;T&gt; input, Action&lt;T&gt; act) { foreach (var item in input) ThreadPool.QueueUserWorkItem(obj =&gt; act((T)obj), item); return input; } </code></pre>
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