using System;

using System.Linq;

​

    public class Program

    {

        public static void Main(string[] args)

        {

            var tests1 = new[] { new TestWithOverride(1), new TestWithOverride(2), new TestWithOverride(3) };

​

            var contains = tests1.Contains(new TestWithOverride(2));

​

            Console.WriteLine(contains);

​

            var tests2 = new[] { new TestWithoutOverride(1), new TestWithoutOverride(2), new TestWithoutOverride(3) };

​

            contains = tests2.Contains(new TestWithoutOverride(2));

​

            Console.WriteLine(contains);

        }

    }

​

    internal class TestWithOverride : IEquatable<TestWithOverride>

    {

        public TestWithOverride(int id)

        {

            Id = id;

        }

​

        public int Id { get;}

​

        public bool Equals(TestWithOverride other) => this.Id == other.Id;

​

        public override bool Equals(object obj)

        {

            var test = obj as TestWithOverride;

​

            return test == null ? obj.Equals(this) : Equals(test);

        }

    }

​

    internal class TestWithoutOverride : IEquatable<TestWithoutOverride>

    {

        public TestWithoutOverride(int id)

        {

            Id = id;

        }

​

        public int Id { get;}

​

        public bool Equals(TestWithoutOverride other) => this.Id == other.Id;

    }