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POInvalidCastException on Generics
 

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    <p>Coming from the Java world, programming with generics and C# is often a headache. Like this one:</p> <pre><code>interface ISomeObject { } class SomeObjectA : ISomeObject { } class SomeObjectB : ISomeObject { } interface ISomething&lt;T&gt; where T : ISomeObject { T GetObject(); } class SomethingA : ISomething&lt;SomeObjectA&gt; { public SomeObjectA GetObject() { return new SomeObjectA(); } } class SomethingB : ISomething&lt;SomeObjectB&gt; { public SomeObjectB GetObject() { return new SomeObjectB(); } } class SomeContainer { private ISomething&lt;ISomeObject&gt; Something; public void SetSomething&lt;T&gt;(ISomething&lt;T&gt; s) where T : ISomeObject { Something = (ISomething&lt;ISomeObject&gt;)s; } } class TestContainerSomething { static public void Test() { SomeContainer Container = new SomeContainer(); Container.SetSomething&lt;SomeObjectA&gt;(new SomethingA()); } } </code></pre> <p>Which results into an <code>InvalidCastException</code> at <code>Something = (ISomething&lt;ISomeObject&gt;)s;</code>. In Java, this would work, and I could even use (if all else fails) the generics wildcard <code>&lt;?&gt;</code>. This is not possible in C#. </p> <p>While this is just an example that I put together to explain the problematic, how can this exception be eliminated? The only main constraint is that <code>SomeContainer</code> <strong>cannot</strong> be a generic class</p> <p>** <strong>Note</strong> ** : there are many questions about this, but none of them (that I could find) address a generic class member inside a non generic class.</p> <p>** <strong>Update</strong> **</p> <p>Inside the method <code>SetSomething</code>, I added these lines :</p> <pre><code>Console.WriteLine(s.GetType().IsSubclassOf(typeof(ISomething&lt;SomeObjectA&gt;))); Console.WriteLine(s.GetType().ToString() + " : " + s.GetType().BaseType.ToString()); foreach (var i in s.GetType().GetInterfaces()) { Console.WriteLine(i.ToString()); } </code></pre> <p>which to my surprise output</p> <pre><code>False SomeThingA : System.Object ISomething`1[SomeObjectA] </code></pre> <p>Is this why I get this exception?</p>
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