using System;

using System.Linq;

using System.Collections.Generic;

public static class Program {

    public static bool IsIEnumerableOfT (this Type type) =>

        type.GetInterfaces().Any(x => x.IsGenericType && x.GetGenericTypeDefinition() == typeof(IEnumerable<>));

​

    static bool Test <T> (T obj) => typeof(T).IsIEnumerableOfT();

​

    public static void Main () {

​

        Console.WriteLine(typeof(List<int>).IsIEnumerableOfT());

        Console.WriteLine(typeof(IList<int>).IsIEnumerableOfT());

        Console.WriteLine(typeof(IEnumerable<int>).IsIEnumerableOfT()); // <- fails

        List<int> obj = new List<int>();

        Console.WriteLine(Test(obj));

​

        IEnumerable<int> e = obj;

        Console.WriteLine(Test(e)); // <- fails

    }

}