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copied!<p><a href="https://stackoverflow.com/a/74648/1968">The previously accepted answer</a> is nice but it is wrong. Thankfully, the error is a small one. Checking for <code>IEnumerable</code> is not enough if you really want to know about the generic version of the interface; there are a lot of classes that implement only the nongeneric interface. I'll give the answer in a minute. First, though, I'd like to point out that the accepted answer is overly complicated, since the following code would achieve the same under the given circumstances:</p> <pre><code>if (items[key] is IEnumerable) </code></pre> <p>This does even more because it works for each item separately (and not on their common subclass, <code>V</code>).</p> <p>Now, for the correct solution. This is a bit more complicated because we have to take the generic type <code>IEnumerable`1</code> (that is, the type <code>IEnumerable<></code> with one type parameter) and inject the right generic argument:</p> <pre><code>static bool IsGenericEnumerable(Type t) { var genArgs = t.GetGenericArguments(); if (genArgs.Length == 1 && typeof(IEnumerable<>).MakeGenericType(genArgs).IsAssignableFrom(t)) return true; else return t.BaseType != null && IsGenericEnumerable(t.BaseType); } </code></pre> <p>You can test the correctness of this code easily:</p> <pre><code>var xs = new List<string>(); var ys = new System.Collections.ArrayList(); Console.WriteLine(IsGenericEnumerable(xs.GetType())); Console.WriteLine(IsGenericEnumerable(ys.GetType())); </code></pre> <p>yields:</p> <pre><code>True False </code></pre> <p>Don't be overly concerned by the fact that this uses reflection. While it's true that this adds runtime overhead, so does the use of the <code>is</code> operator.</p> <p>Of course the above code is awfully constrained and could be expanded into a more generally applicable method, <code>IsAssignableToGenericType</code>. The following implementation is slightly incorrect<sup>1</sup> and I’ll leave it here <em>for historic purposes only</em>. <strong>Do not use it</strong>. Instead, <a href="https://stackoverflow.com/a/1075059/1968">James has provided an excellent, correct implementation in his answer.</a></p> <pre><code>public static bool IsAssignableToGenericType(Type givenType, Type genericType) { var interfaceTypes = givenType.GetInterfaces(); foreach (var it in interfaceTypes) if (it.IsGenericType) if (it.GetGenericTypeDefinition() == genericType) return true; Type baseType = givenType.BaseType; if (baseType == null) return false; return baseType.IsGenericType && baseType.GetGenericTypeDefinition() == genericType || IsAssignableToGenericType(baseType, genericType); } </code></pre> <p><sup>1</sup> It fails when the <code>genericType</code> is the same as <code>givenType</code>; for the same reason, it fails for nullable types, i.e.</p> <pre><code>IsAssignableToGenericType(typeof(List<int>), typeof(List<>)) == false IsAssignableToGenericType(typeof(int?), typeof(Nullable<>)) == false </code></pre> <p>I’ve created a <a href="https://gist.github.com/4174727" rel="nofollow noreferrer">gist with a comprehensive suite of test cases</a>.</p>

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