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    <p>The various answers here have sussed it out. To sum up and provide some links to explanatory material:</p> <p>First, the literal zero is convertible to any enum type. The reason for this is because we want you to be able to initialize any "flags" enum to its zero value even if there is no zero enum value available. (If we had to do it all over again we'd probably not implement this feature; rather, we'd say to just use the <code>default(MyEnum)</code> expression if you want to do that.)</p> <p>In fact, the <em>constant</em>, not just the <em>literal constant</em> zero is convertible to any enum type. This is for backwards compatibility with a historic compiler bug that is more expensive to fix than to enshrine.</p> <p>For more details, see</p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2006/03/28/the-root-of-all-evil-part-one.aspx">http://blogs.msdn.com/b/ericlippert/archive/2006/03/28/the-root-of-all-evil-part-one.aspx</a></p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2006/03/29/the-root-of-all-evil-part-two.aspx">http://blogs.msdn.com/b/ericlippert/archive/2006/03/29/the-root-of-all-evil-part-two.aspx</a></p> <p>That then establishes that your two indexers -- one which takes an int and one which takes an enum -- are both applicable candidates when passed the literal zero. The question then is which is the <em>better</em> candidate. The rule here is simple: if any candidate is applicable in a derived class then it is automatically better than any candidate in a base class. Therefore your enum indexer wins.</p> <p>The reason for this somewhat counter-intuitive rule is twofold. First, it seems to make sense that <em>the person who wrote the derived class has more information than the person who wrote the base class</em>. They specialized the base class, after all, so it seems reasonable that you'd want to call the <em>most specialized implementation possible</em> when given a choice, even if it is not an exact match.</p> <p>The second reason is that this choice mitigates the brittle base class problem. If you added an indexer <em>to a base class</em> that happened to be a better match than one on a derived class, it would be unexpected to users of the derived class that code that used to choose the derived class suddenly starts choosing the base class. </p> <p>See </p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2007/09/04/future-breaking-changes-part-three.aspx">http://blogs.msdn.com/b/ericlippert/archive/2007/09/04/future-breaking-changes-part-three.aspx</a></p> <p>for more discussion of this issue.</p> <p>As James correctly points out, if you make a new indexer on your class that takes an int then the overload resolution question becomes which is better: conversion from zero to enum, or conversion from zero to int. Since both indexers are on the same type and the latter is <em>exact</em>, it wins.</p>
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    1. POOverloaded indexer with enum : impossible to use default indexer
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    1. COThanks for all the links and the explanation, I was in fact facing two problems : the "0" literal behavior combined with inheritance and method resolution.
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