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POCompiler Ambiguous invocation error - anonymous method and method group with Func<> or Action
 

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  1. POCompiler Ambiguous invocation error - anonymous method and method group with Func<> or Action
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    <p>I have a scenario where I want to use method group syntax rather than anonymous methods (or lambda syntax) for calling a function.</p> <p>The function has two overloads, one that takes an <code>Action</code>, the other takes a <code>Func&lt;string&gt;</code>.</p> <p>I can happily call the two overloads using anonymous methods (or lambda syntax), but get a compiler error of <em>Ambiguous invocation</em> if I use method group syntax. I can workaround by explicit casting to <code>Action</code> or <code>Func&lt;string&gt;</code>, but don't think this should be necessary.</p> <p>Can anyone explain why the explicit casts should be required.</p> <p>Code sample below.</p> <pre><code>class Program { static void Main(string[] args) { ClassWithSimpleMethods classWithSimpleMethods = new ClassWithSimpleMethods(); ClassWithDelegateMethods classWithDelegateMethods = new ClassWithDelegateMethods(); // These both compile (lambda syntax) classWithDelegateMethods.Method(() =&gt; classWithSimpleMethods.GetString()); classWithDelegateMethods.Method(() =&gt; classWithSimpleMethods.DoNothing()); // These also compile (method group with explicit cast) classWithDelegateMethods.Method((Func&lt;string&gt;)classWithSimpleMethods.GetString); classWithDelegateMethods.Method((Action)classWithSimpleMethods.DoNothing); // These both error with "Ambiguous invocation" (method group) classWithDelegateMethods.Method(classWithSimpleMethods.GetString); classWithDelegateMethods.Method(classWithSimpleMethods.DoNothing); } } class ClassWithDelegateMethods { public void Method(Func&lt;string&gt; func) { /* do something */ } public void Method(Action action) { /* do something */ } } class ClassWithSimpleMethods { public string GetString() { return ""; } public void DoNothing() { } } </code></pre>
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    1. USRichard Everett
    1. USRichard Everett
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    1. COI have tried your code and I'm getting an additional compile time error: 'void test.ClassWithSimpleMethods.DoNothing()' has the wrong return type (which is on line 25, which is where the ambiguity error is)
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      1. POCompiler Ambiguous invocation error - anonymous method and method group with Func<> or Action
      1. USMatt Ellen
    2. CO@Matt: I see that error as well. The errors I cited in my post were the compilation issues that VS highlights before you even try a full compile.
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      1. POCompiler Ambiguous invocation error - anonymous method and method group with Func<> or Action
      1. USRichard Everett
    3. COBy the way, this was a great question. I love anything which forces me into the specs :)
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      1. USJon Skeet
 

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