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POSomeList<T> : List<T> can't be cast as List<T>?
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  1. POSomeList<T> : List<T> can't be cast as List<T>?
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    copied!<p>See comment in Main(). Why can't I perform the following?</p> <pre><code> public class SomeList&lt;T&gt; : List&lt;T&gt; { public SomeList(List&lt;T&gt; existing) { foreach (var item in existing) Add(item); } public override string ToString() { return "I'm a better list."; } } internal interface IReadStuff&lt;T&gt; { List&lt;T&gt; ReadStuff(); } public class ReaderStrategy&lt;Foo&gt; : IReadStuff&lt;Foo&gt; { public List&lt;Foo&gt; ReadStuff() { return new List&lt;Foo&gt;(); } } public class Foo {} public class Main { public Main() { var reader = new ReaderStrategy&lt;Foo&gt;(); // This works, but type is List&lt;Foo&gt;, not SomeList&lt;Foo&gt; List&lt;Foo&gt; aList = reader.ReadStuff(); // This does not compile, but is what I want to do: SomeList&lt;Foo&gt; aBetterList = reader.ReadStuff(); // This compiles, but always generates null for aBetterList: SomeList&lt;Foo&gt; anotherBetterList = reader.ReadStuff() as SomeList&lt;Foo&gt;; // This is funky but works: SomeList&lt;Foo&gt; works = new SomeList&lt;Foo&gt;(reader.ReadStuff()); } } </code></pre> <p>I am struggling understanding how to use generics with inherited types. I have a need for the above because I want to extend the functionality of <code>List&lt;T&gt;</code> is some special way, for example see <code>SomeList&lt;T&gt; overrides ToString()</code>. However, I want to keep my factory strategy using .Net generic <code>List&lt;T&gt;</code>. Is there a way to make this work?</p> <p><strong>Edit</strong></p> <p>I added a constructor that accepts <code>List&lt;T&gt;</code> and adds to <code>SomeList&lt;T&gt;</code>. This doesn't seem natural, but works. This is an expensive operation, especially if <code>List&lt;T&gt;</code> is large. </p> <p>My question title was not the best, what I was striving for was an example showing a better way to do this.</p>
 

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