using System;

using System.Collections.Generic;

​

namespace App {

​

    using ExtensionMethods;

    public class Program

    {

        public static void Main()

        {

            List<ExampleClass1> exampleClasses1 = new List<ExampleClass1>(); //IEnumerable ? IReadOnlyCollection

            List<ExampleClass2> exampleClasses2 = new List<ExampleClass2>(); //IEnumerable ? IReadOnlyCollection

            List<IExampleInterface> onlyTrue = exampleClasses1.GetTrue(); //nazwa metody

            onlyTrue.AddRange(exampleClasses2.GetTrue());

            Console.WriteLine("Done");

​

            //TODO: Write extension method GetTrue() for Lists of classes implementing IExampleInterface

​

        }

    }

        public interface IExampleInterface 

        {

            bool IsTrue {get; set;}

        }

​

        public class ExampleClass1 : IExampleInterface

        {

            public bool IsTrue { get; set; }

        }

​

        public class ExampleClass2 : IExampleInterface

        {

            public bool IsTrue { get; set; }

        }   

}

​

​

namespace ExtensionMethods

{

    using App;

    public static class InterfaceExtensions {       

        public static List<IExampleInterface> GetTrue<T>(this List<T> classes) where T: IExampleInterface

        {

            List<IExampleInterface> interfaces = new List<IExampleInterface>();

            foreach(var item in classes)

            {

                if (item is IExampleInterface)

                {

                    interfaces.Add(item);

                }

            }

            return interfaces;

        }

    }

}