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    <p><strong>Update</strong>: Your problem is not related to the <code>yield</code> keyword specifically. It has to do with <strong>type variance</strong>.</p> <p>Your <code>AcceptChangesAndYield</code> method returns an object of a type implementing <code>IEnumerable&lt;MyModels.Interfaces.ILookup&gt;</code> (in fact it is a compiler-generated type, but that's not really important). In your method call you are trying to <em>downcast</em> this to an <code>IEnumerable&lt;MyModels.StatusLookup&gt;</code>, which is <em>more specific</em>.</p> <p>The <code>IEnumerable&lt;T&gt;</code> interface is <strong>covariant</strong> which would allow you to <em>upcast</em> to a <em>less specific</em> type; e.g., you could cast from a <code>List&lt;string&gt;</code> to an <code>IEnumerable&lt;object&gt;</code> (in .NET 4.0, anyway). The type generated by the compiler to supply the return value of your <code>AcceptChangesAndYield</code> method only implements <code>IEnumerable&lt;MyModels.Interfaces.ILookup&gt;</code>, so you could cast the result to an <code>IEnumerable&lt;object&gt;</code> (for instance), but <em>not</em> to an <code>IEnumerable&lt;MyModels.StatusLookup&gt;</code>.</p> <p>Fortunately, the solution is pretty simple. Redefine your <code>AcceptChangesAndYield</code> method as follows:</p> <pre><code>// Note: We are using a generic type constraint on T. public static IEnumerable&lt;T&gt; AcceptChangesAndYield&lt;T&gt;(this IEnumerable&lt;T&gt; obj) where T : MyModels.Interfaces.ILookup { if (obj.IsNull()) yield break; foreach (var m in obj) { // Did you mean to put m.AcceptChanges() here? yield return m; } } </code></pre> <p>This will in turn allow your <code>GetAll</code> method to be implemented as follows:</p> <pre><code>public IEnumerable&lt;MyModels.StatusLookup&gt; GetAll() { var results = Database.Current.pStatusLookupLoadAll() .ExecuteTypedList&lt;MyModels.StatusLookup&gt;(); // Note: no need for a cast, as the return value is now // already strongly typed as IEnumerable&lt;MyModels.StatusLookup&gt;. return results.AcceptChangesAndYield(); } </code></pre> <hr> <p><strong>Original Answer</strong>: It seems like you just want this?</p> <pre><code>IEnumerable&lt;T&gt; EnumerateResults&lt;T&gt;(IEnumerable&lt;T&gt; results) { if (results.IsNull()) yield break; foreach (T result in results) { // ..Common logic lines... yield return result; } } </code></pre> <p>Then in your code where you want to remove duplication, you'd just have:</p> <pre><code>// Specific stuff var results = BlahBlahBlah(); // Common stuff return EnumerateResults(results); </code></pre> <p>Right? Or am I misunderstanding your problem?</p>
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    1. POExtract yield lines into common method
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    1. USDan Tao
    1. USDan Tao
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    1. COyou are spot on what I am trying to do. I'll post an "answer" with what I am getting when I try that.
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    2. COoriginal post edited with what I tried and my current problem. Thx
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    3. CO@David W: After looking at your update to the question I'm pretty sure I understand the problem you're running into. Try out the suggestion I've made in my update and let me know if that helps!
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