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    <p>No, there's no individual signature that can do this - there's no way of saying "the nullable type of <code>R</code>, which is either <code>R</code> itself for a reference type, or <code>Nullable&lt;R&gt;</code> for a non-nullable value type".</p> <p>You can have different methods, each with a different constraint on <code>R</code> - but then you either have to provide different names, or use <a href="http://codeblog.jonskeet.uk/2010/11/02/evil-code-overload-resolution-workaround/" rel="nofollow"><em>horrible hacks</em></a> to <em>effectively</em> overload by type parameter constraints.</p> <p>I suspect you should basically have two different method names here, for simplicity. So signatures of:</p> <pre><code>public static Nullable&lt;R&gt; GetValue&lt;T, R&gt;(this T a, Expression&lt;Func&lt;T, R&gt;&gt; expression) where T : Attribute where R : struct public static R GetReference&lt;T, R&gt;(this T a, Expression&lt;Func&lt;T, R&gt;&gt; expression) where T : Attribute where R : class </code></pre> <p>Two asides:</p> <ul> <li>Conventionally type parameters start with <code>T</code>, e.g. <code>TInput</code> and <code>TResult</code></li> <li>Why are you using expression trees at all for <code>GetValue</code>? Why not just take a <code>Func&lt;T, R&gt;</code> and execute it? </li> </ul> <p>As an example of the second bullet point:</p> <pre><code>public static Nullable&lt;R&gt; GetValue&lt;T, R&gt;(this T a, Func&lt;T, R&gt; func) where T : Attribute where R : struct { if (a == null) return null; return func(a); } </code></pre>
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    1. POCan I create a generic method that takes a value type or a reference type but always returns a nullable type
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    1. USRJ Cuthbertson
    1. USJon Skeet
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    1. COI thought that might be the case, Jon. I'm using an expression tree bcause that appears to be the most common way that people go about getting a PropertyInfo using lambdas rather than magic strings, not because I really understand it. If I promise to go back and read that chapter in your book again will you show me an example of what you mean now? ;-)
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    2. CO@Colin: Sure, will edit that in.
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    3. CONote that if you have these two methods you can accept any object that a method without either constraint could *except for a nullable struct*. You need to add a third overload where `T` is a nullable struct to really get everything.
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