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POOverloaded method-group argument confuses overload resolution?
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copied!<p>The following call to the overloaded <a href="http://msdn.microsoft.com/en-us/library/system.linq.enumerable.select.aspx" rel="noreferrer"><strong><code>Enumerable.Select</code></strong></a> method:</p> <pre><code>var itemOnlyOneTuples = "test".Select<char, Tuple<char>>(Tuple.Create); </code></pre> <p>fails with an ambiguity error (namespaces removed for clarity):</p> <pre><code>The call is ambiguous between the following methods or properties: 'Enumerable.Select<char,Tuple<char>> (IEnumerable<char>,Func<char,Tuple<char>>)' and 'Enumerable.Select<char,Tuple<char>> (IEnumerable<char>, Func<char,int,Tuple<char>>)' </code></pre> <p>I can certainly understand why <em>not</em> specifying the type-arguments explicitly would result in an ambiguity (both the overloads would apply), but I don't see one after doing so.</p> <p>It appears clear enough to me that the intention is to call the first overload, with the method-group argument resolving to <code>Tuple.Create<char>(char)</code>. The second overload should not apply because none of the <code>Tuple.Create</code> overloads can be converted to the expected <code>Func<char,int,Tuple<char>></code> type. I'm <em>guessing</em> the compiler is confused by <code>Tuple.Create<char, int>(char, int)</code>, but its return-type is wrong: it returns a two-tuple, and is hence not convertible to the relevant <code>Func</code> type.</p> <p>By the way, any of the following makes the compiler happy:</p> <ol> <li>Specifying a type-argument for the method-group argument: <code>Tuple.Create<char></code> (Perhaps this is actually a type-inference issue?).</li> <li>Making the argument a lambda-expression instead of a method-group: <code>x => Tuple.Create(x)</code>. (Plays well with type-inference on the <code>Select</code> call).</li> </ol> <p>Unsurprisingly, trying to call the other overload of <code>Select</code> in this manner also fails:</p> <pre><code>var itemIndexTwoTuples = "test".Select<char, Tuple<char, int>>(Tuple.Create); </code></pre> <p>What's the exact problem here?</p>

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