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copied!<p><em>Note: Not really an answer, but far too big for a comment.</em></p> <p>More interesting results when you throw in type-inference. Consider this code:</p> <pre><code>public class Test { public static void Blah<T>(Action<T> blah) { } public static void Main() { Blah(x => { Console.LineWrite(x); }); } } </code></pre> <p>It won't compile, because there's no good way to infer what <code>T</code> should be.<br> <strong>Error Message</strong>:</p> <blockquote> <p>The type arguments for method <code>'Test.Blah<T>(System.Action<T>)'</code> cannot be inferred from the usage. Try specifying the type arguments explicitly.</p> </blockquote> <p>Makes sense. Let's specify the type of <code>x</code> explicitly and see what happens:</p> <pre><code>public static void Main() { Blah((int x) => { Console.LineWrite(x); }); } </code></pre> <p>Now things go awry because <code>LineWrite</code> doesn't exist.<br> <strong>Error Message</strong>:</p> <blockquote> <p>'System.Console' does not contain a definition for 'LineWrite'</p> </blockquote> <p>Also sensible. Now let's add in named arguments and see what happens. First, without specifying the type of <code>x</code>:</p> <pre><code>public static void Main() { Blah(blah: x => { Console.LineWrite(x); }); } </code></pre> <p>We would expect to get an error message about not being able to infer type arguments. And we do. <em>But that's not all</em>.<br> <strong>Error Messages</strong>:</p> <blockquote> <p>The type arguments for method <code>'Test.Blah<T>(System.Action<T>)'</code> cannot be inferred from the usage. Try specifying the type arguments explicitly.</p> <p>'System.Console' does not contain a definition for 'LineWrite'</p> </blockquote> <p>Neat. Type inference fails, <em>and</em> we're told exactly why the lambda conversion failed. Ok, so let's specify the type of <code>x</code> and see what we get:</p> <pre><code>public static void Main() { Blah(blah: (int x) => { Console.LineWrite(x); }); } </code></pre> <p><strong>Error Messages</strong>:</p> <blockquote> <p>The type arguments for method <code>'Test.Blah<T>(System.Action<T>)'</code> cannot be inferred from the usage. Try specifying the type arguments explicitly.</p> <p>'System.Console' does not contain a definition for 'LineWrite'</p> </blockquote> <p>Now <em>that</em> is unexpected. Type inference is still failing (I assume because the lambda -> <code>Action<T></code> conversion is failing, thus negating the compiler's guess that <code>T</code> is <code>int</code>) <em>and</em> reporting the cause of the failure.</p> <p><strong>TL; DR</strong>: I'll be glad when Eric Lippert gets around to looking at the heuristics for these more complex cases.</p>

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