using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var result = new List<EquatableStruct> { new EquatableStruct() }.Contains(new EquatableStruct());

        Console.WriteLine(result);

        result = new List<PlainStruct> { new PlainStruct() }.Contains(new PlainStruct());

        Console.WriteLine(result);

    }

}

​

public struct EquatableStruct : IEquatable<EquatableStruct>

{

    public bool Equals(EquatableStruct other)

    {

        Console.WriteLine("non-boxed Equals called.");

        return true;

    }

    public override bool Equals(object other)

    {

        Console.WriteLine("boxed Equals called.");

        return true;

    }

    public override int GetHashCode()

    {

        return 0;

    }

}

​

public struct PlainStruct

{

    public bool Equals(EquatableStruct other)

    {

        Console.WriteLine("non-boxed Equals called.");

        return true;

    }

    public override bool Equals(object other)

    {

        Console.WriteLine("boxed Equals called.");

        return true;

    }

    public override int GetHashCode()

    {

        return 0;

    }

}