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    <p>This happens because you are not overloading the method and nor is the base method declared virtual, so virtual method dispatch is not used. This means that method calls will be bound at compile-time, and so <em>type of the reference</em> used to call the method will determine which method is called, instead of the <em>type of the referenced object</em>.</p> <p>You should get a warning on the line declaring <code>foo()</code> within <code>Specific</code> since it hides the member from the parent type and you have not specified <code>new</code>. Pay attention to warnings!</p> <p>To resolve this issue, declare the method in <code>Generic</code> as <code>virtual</code>:</p> <pre><code>public virtual String foo(M n) </code></pre> <p>And override it in <code>Specific</code>:</p> <pre><code>public override String foo(M n) </code></pre> <p>In this case, the call will be bound to a specific override of this method at runtime, using the vtable of the actual object the method is invoked on.</p> <p>Note that an override can't change the types of parameters of the method being overridden, so you cannot declare the <code>foo()</code> in <code>Specific</code> to accept an <code>N</code> object. However, you can specify an additional <em>overload</em> if desired. The <code>foo(M)</code> overload may need to look at the type of the passed object to determine what to do with it. (Or, even better, make <code>foo(M)</code> <em>not care</em> if it was passed an <code>M</code> or an <code>N</code>.)</p> <p>Possible implementation of an override that should only accept <code>N</code> (though this smells of bad design):</p> <pre><code>public override String foo(M m) { if (m == null) { throw new ArgumentNullException("m"); } N n = m as N; if (n == null) { throw new ArgumentException("Must be an N instance.", "m"); } return foo(n); } public virtual String foo(N n) { // Use the n variable } </code></pre>
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    1. CO`Generic.foo` and `Specific.foo` have different signatures! (M vs. N)
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    2. CO@ffel I already edited my answer to address this. You can't override this way, unless you use generics as per Alessandro's answer. But be careful with that approach so that you don't wind up with a base class with a hundred different generic type parameters!
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    3. COEventually, I've come up with a solution that is more or less equivalent to your suggestion. My code is happily accepted by both xamarin as well as vs, though.
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