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POGeneric extension methods in C#: what will happen in this edge case?
 

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  1. POGeneric extension methods in C#: what will happen in this edge case?
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    <p>In a recent <a href="https://stackoverflow.com/questions/3255450/anti-constraint-on-c-generics">question of mine</a> I learned that if there are more than one extension methods with constraints that match the given type, the most specific one will be chosen. This got me thinking - how does the compiler determine which one is "more specific"? And what will the outcome be?</p> <p>Let's say I have the following classes:</p> <pre><code>public MyClass : IComparable, IDisposable { // Implementation of members } public static class MyExtensions { public static void DoSomething&lt;T&gt;(this T item) where T : IComparable { /* whatever */ } public static void DoSomething&lt;T&gt;(this T item) where T : IDisposable { /* whatever else */ } } </code></pre> <p>If I now use the extension method as </p> <pre><code>var instance = new MyClass(); instance.DoSomething(); </code></pre> <p>which method will be used? Or will the compiler throw an error?</p> <p>Note: I'm not saying this is good design, or even that I have a case where I need to do this. But the term "more specific" was loose enough to make me ponder this, and now I have to know! :P</p> <p><strong>Update:</strong> I guess I wasn't really as interested in <em>what</em> will happen in the above example, as in <em>why</em>. It came to my mind since I'd been doing stuff like</p> <pre><code>public static class CollectionExtensions { public static void DoSomething&lt;T&gt;(this T items) where T : IList { ... } public static void DoSomething&lt;T&gt;(this T items) where T : IEnumerable { ... } } </code></pre> <p>where the compiler knows to choose the first method for <code>new List&lt;Something&gt;().DoSomething()</code>, since it is "closer" to the type passed. What I was interested in then, was "what does <em>closer</em> in this context mean? How will the compiler react if the constraints are from two different inheritance chains? Why?"</p>
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    1. USTomas Lycken
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    1. COI'm surprised you didn't try/compile this code before asking the question. The compiler gives a very reasonable justification to not compile this code. or what else are you looking for besides the normal answer.
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    2. COI was interested in more details on *why* the compiler can't do this, rather than just the fact that it can't. For some reason, I expected there to be more intricate reasons behind this, but judging by the answers it seems I made this more complicated than it is when thinking about it.
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    3. COplease check my answer now.
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