El Doble Rasero del Operador `==` en C#

using System;

public class Money
{
    public decimal Amount { get; }
    public string Currency { get; }

    public Money(decimal amount, string currency)
    {
        Amount = amount;
        Currency = currency;
    }

    public static bool operator ==(Money? m1, Money? m2)
    {
        if (ReferenceEquals(m1, m2))
            return true;
        if (ReferenceEquals(m1, null) || ReferenceEquals(m2, null))
            return false;
        return m1.Amount == m2.Amount && m1.Currency == m2.Currency;
    }

    public static bool operator !=(Money? m1, Money? m2)
    {
        return !(m1 == m2);
    }

    public override bool Equals(object? obj)
    {
        if (obj is not Money other) return false;
        return Amount == other.Amount && Currency == other.Currency;
    }

    public override int GetHashCode()
    {
        return HashCode.Combine(Amount, Currency);
    }
}

public class Program
{
    public static void Main()
    {
        Money cash1 = new Money(100.00m, "USD");
        Money cash2 = new Money(100.00m, "USD");

        Console.WriteLine($"cash1 == cash2: {cash1 == cash2}");
        Console.WriteLine($"((object)cash1) == ((object)cash2): {((object)cash1) == ((object)cash2)}");
    }
}