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    <p>I would say that the correct answer to the question is given by E.Lippert in <a href="https://stackoverflow.com/questions/4965576/why-cant-an-anonymous-method-be-assigned-to-var">SO Why can't an anonymous method be assigned to var?</a></p> <p>But let us play with your example a little:</p> <pre><code>Func&lt;Func&lt;int&gt;&gt; f = () =&gt; { int i = 0; return () =&gt; i; }; Func&lt;int&gt; x = Test(f); //it compiles OK </code></pre> <p>No problem in type inference with your <code>Func&lt;T&gt; Test&lt;T&gt;(Func&lt;Func&lt;T&gt;&gt; func)</code> here. The problem is hidden in that you use an anonymous lambda expression, the type of which cannot be inferred. Try this:</p> <pre><code>var f = () =&gt; { int i = 0; return () =&gt; i; }; </code></pre> <p>It gives <a href="http://msdn.microsoft.com/en-us/library/bb384140%28v=vs.90%29.aspx" rel="nofollow noreferrer">Compiler Error CS0815</a>, saying</p> <blockquote> <p>Cannot assign lambda expression to an implicitly-typed local variable</p> </blockquote> <p>and the explanation is:</p> <blockquote> <p>An expression that is used as the initializer for an implicitly typed variable must have a type. Because anonymous function expressions, method group expressions, and the null literal expression do not have a type, they are not appropriate initializers. An implicitly typed variable cannot be initialized with a null value in its declaration, although it can later be assigned a value of null.</p> </blockquote> <p>Now let's try another thing: </p> <pre><code>var x = Test(() =&gt; { Func&lt;int&gt; f = () =&gt; 0; return f; }); </code></pre> <p>It compiles as well. So the problem with your original example was actually with this line:</p> <pre><code>return () =&gt; i; </code></pre> <p>We can go further and according to what Eric Lippert says in his answer provide another function to wrap this:</p> <pre><code>static Func&lt;T&gt; GetFunc&lt;T&gt;(Func&lt;T&gt; f) { return f; } </code></pre> <p>Now we can rewrite your code like:</p> <pre><code>var x = Test(() =&gt; { int i = 0; return GetFunc(() =&gt; i); }); </code></pre> <p>And it works as well.</p> <p>However, as far as I understand, this all is an overhead and you should just provide an explicit type. While these workarounds are suitable, when you need to have a lambda, returning an object of anonymous type.</p>
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