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POWrong overload is overridden when two methods have identical signatures after substitution of type arguments
 

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  1. POWrong overload is overridden when two methods have identical signatures after substitution of type arguments
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    <p>We believe this example exhibits a bug in the C# compiler (do make fun of me if we are wrong). This bug may be well-known: After all, our example is a simple modification of what is described <a href="http://blogs.msdn.com/b/samng/archive/2008/02/13/generic-method-substitutions-and-unification.aspx" rel="noreferrer">in this blog post</a>.</p> <pre><code>using System; namespace GenericConflict { class Base&lt;T, S&gt; { public virtual int Foo(T t) { return 1; } public virtual int Foo(S s) { return 2; } public int CallFooOfT(T t) { return Foo(t); } public int CallFooOfS(S s) { return Foo(s); } } class Intermediate&lt;T, S&gt; : Base&lt;T, S&gt; { public override int Foo(T t) { return 11; } } class Conflict : Intermediate&lt;string, string&gt; { public override int Foo(string t) { return 101; } } static class Program { static void Main() { var conflict = new Conflict(); Console.WriteLine(conflict.CallFooOfT("Hello mum")); Console.WriteLine(conflict.CallFooOfS("Hello mum")); } } } </code></pre> <p>The idea is simply to create a class <code>Base&lt;T, S&gt;</code> with two virtual methods whose signatures will become identical after an 'evil' choice of <code>T</code> and <code>S</code>. The class <code>Conflict</code> overloads only one of the virtual methods, and because of the existence of <code>Intermediate&lt;,&gt;</code>, it should be well-defined which one!</p> <p>But when the program is run, the output seems to show that the wrong overload was overridden.</p> <p>When we read Sam Ng's <a href="http://blogs.msdn.com/b/samng/archive/2008/03/04/generic-method-substitutions-and-unification-part-two.aspx" rel="noreferrer">follow-up post</a> we get the expression that that bug was not fixed because they believed a type-load exception would always be thrown. But in our example the code compiles and runs with no errors (just unexpected output).</p>
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    1. USJim Mischel
    1. USJeppe Stig Nielsen
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      1. VTUpMod
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      1. USChris Shain
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      1. VTUpMod
    1. COAssume we don't have a compiler handy - what do you expect as the output, and what *is* the output?
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      1. USMarc Gravell
    2. COAdditionally, what version are you running it on, and does it behave differently in any other versions?
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      1. USServy
    3. COCan you elaborate on the statement: "because of the existence of Intermediate<,>, it should be well-defined which one"?
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      1. USStriplingWarrior
 

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