C# 9.0 新特性之模式匹配简化的实现

public class Car
{
  public int Passengers { get; set; }
}

public class DeliveryTruck
{
  public int GrossWeightClass { get; set; }
}

public class Taxi
{
  public int Fares { get; set; }
}

public class Bus
{
  public int Capacity { get; set; }
  public int Riders { get; set; }
}

public decimal CalculateToll(object vehicle) =>
  vehicle switch
{
  Car { Passengers: 0}    => 2.00m + 0.50m,
  Car { Passengers: 1}    => 2.0m,
  Car { Passengers: 2}    => 2.0m - 0.50m,
  Car c            => 2.00m - 1.0m,

  Taxi t => t.Fares switch
  {
    0 => 3.50m + 1.00m,
    1 => 3.50m,
    2 => 3.50m - 0.50m,
    _ => 3.50m - 1.00m
  },

  Bus b when ((double)b.Riders / (double)b.Capacity) < 0.50 => 5.00m + 2.00m,
  Bus b when ((double)b.Riders / (double)b.Capacity) > 0.90 => 5.00m - 1.00m,
  Bus b => 5.00m,

  DeliveryTruck t when (t.GrossWeightClass > 5000) => 10.00m + 5.00m,
  DeliveryTruck t when (t.GrossWeightClass < 3000) => 10.00m - 2.00m,
  DeliveryTruck _ => 10.00m,

  { } => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)),
  null => throw new ArgumentNullException(nameof(vehicle))
};

vehicle switch
{
  ...
  Car c => 2.00m - 1.0m
}

vehicle switch
{
  ...
  Car => 2.00m - 1.0m
}

DeliveryTruck t when (t.GrossWeightClass > 5000) => 10.00m + 5.00m,
DeliveryTruck t when (t.GrossWeightClass < 3000) => 10.00m - 2.00m,
DeliveryTruck _ => 10.00m,

DeliveryTruck t when t.GrossWeightClass switch
{
  > 5000 => 10.00m + 5.00m,
  < 3000 => 10.00m - 2.00m,
  _ => 10.00m,
}

DeliveryTruck t when t.GrossWeightClass switch
{
  < 3000 => 10.00m - 2.00m,
  >= 3000 and <= 5000 => 10.00m,
  > 5000 => 10.00m + 5.00m,
}

not null => throw new ArgumentException($"Not a known vehicle type: {vehicle}", nameof(vehicle)),
null => throw new ArgumentNullException(nameof(vehicle))

// 原来的写法
if (!(e is Customer)) { ... }

// 新的写法（易读性更好）
if (e is not Customer) { ... }