using System;

using System.Linq;

using System.Collections.Generic;

using System.Reflection;

​

​

public class Program

{

    public static void Main()

    {       

        var obj = new MyObject();               

        foreach(var m in GetExtMethod(obj.GetType()))

        {

            Console.WriteLine(m.Name);

        }       

    }

    public static IEnumerable<MethodInfo> GetExtMethod(Type classType)

    {

        var typeWhichCanBeExtClass = classType.Assembly.GetTypes()

            .Where(t=>t.IsSealed && !t.IsGenericType && !t.IsNested);

        var typeWithExtMethod = typeWhichCanBeExtClass.SelectMany(t=>t.GetMethods(System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public))

            .Where(m=>m.GetParameters()[0].ParameterType == classType && m.IsDefined(typeof( System.Runtime.CompilerServices.ExtensionAttribute), false));

        return typeWithExtMethod;

    }

}

​

​

​

public static class HelperClass

{

    public static void YesExtMethod(this MyObject obj, String param)

    {

    }

    public static void NoExtMethod(MyObject obj, String param)

    {

    }

}

​

public class MyObject

{

    public void MethodFromMyObject()

    {

    }

}