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copied!<p>As others said, extensions methods are compiler magic, you can alway use VS right click, go to definition to find the real type that implements the static method.</p> <p>From there, it gets <strong>fairly hairy</strong>. <code>Where</code> is overloaded, so you need to find the actual definition that matches the signature you want. <code>GetMethod</code> has some limitations with generic types so you have to find the actual one using a search. </p> <p>Once you find the method, you must make the <code>MethodInfo</code> specific using the <code>MakeGenericMethod</code> call.</p> <p>Here is a full working sample: </p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Reflection; namespace ConsoleApplication9 { class Program { class MyObject { public string Name { get; set; } } public static void CallWhereMethod() { List<MyObject> myObjects = new List<MyObject>() { new MyObject { Name = "Jon Simpson" }, new MyObject { Name = "Jeff Atwood" } }; Func<MyObject, bool> NameEquals = BuildEqFuncFor<MyObject>("Name", "Jon Simpson"); // The Where method lives on the Enumerable type in System.Linq var whereMethods = typeof(System.Linq.Enumerable) .GetMethods(BindingFlags.Static | BindingFlags.Public) .Where(mi => mi.Name == "Where"); Console.WriteLine(whereMethods.Count()); // 2 (There are 2 methods that are called Where) MethodInfo whereMethod = null; foreach (var methodInfo in whereMethods) { var paramType = methodInfo.GetParameters()[1].ParameterType; if (paramType.GetGenericArguments().Count() == 2) { // we are looking for Func<TSource, bool>, the other has 3 whereMethod = methodInfo; } } // we need to specialize it whereMethod = whereMethod.MakeGenericMethod(typeof(MyObject)); var ret = whereMethod.Invoke(myObjects, new object[] { myObjects, NameEquals }) as IEnumerable<MyObject>; foreach (var item in ret) { Console.WriteLine(item.Name); } // outputs "Jon Simpson" } public static Func<T, bool> BuildEqFuncFor<T>(string prop, object val) { return t => t.GetType().InvokeMember(prop, BindingFlags.GetProperty, null, t, null) == val; } static void Main(string[] args) { CallWhereMethod(); Console.ReadKey(); } } } </code></pre>

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