14. Object equality, GetHashCode and ToString

public sealed class Money : IEquatable<Money>
{
    public decimal Amount { get; }
    public string Currency { get; }
    public Money(decimal amount, string currency) => (Amount, Currency) = (amount, currency);

    public bool Equals(Money? other) => other is not null && Amount == other.Amount && Currency == other.Currency;
    public override bool Equals(object? obj) => Equals(obj as Money);
    public override int GetHashCode() => HashCode.Combine(Amount, Currency);
    public override string ToString() => $"{Amount} {Currency}";
}
// Or simply: public record Money(decimal Amount, string Currency);  — generates all of the above