LINQ Where Duck Typing Test http://ericlippert.com/2014/01/02/what-is-duck-typing/comment-page-1/

new_gist_file.cs

using System;

class Customer
{
	public string City { get; set; }
}

class Customers
{
	private Customer c;
	
	public Customers()
	{
		c = new Customer();
		c.City = "New York";
	}
	
	public Customer Where(Func<Customer, bool> predicate)
	{
		if (predicate(c) == true)
			return c;
		else
			return null;
	}
}

public class Program
{
	public static void Main()
	{
		var customers = new Customers();
		
		var list = from c in customers where c.City == "London" select c;
		
		Console.WriteLine("Hello World " + ((list != null) ? list.ToString() : "null"));
	}
}