public decimal CalculateDiscount(Order order) =>
order switch
{
(Items: > 10, Cost: > 1000.00m) => 0.10m,
(Items: > 5, Cost: > 500.00m) => 0.05m,
Order { Cost: > 250.00m } => 0.02m,
null => throw new ArgumentNullException(nameof(order), "Can't calculate discount on null order"),
var someObject => 0m,
};