C# new syntax

Question

see the below code and tell me is it a regular function CalculateToll() whose syntax is now bit different ?

public class TollCalculator  
{  
    public decimal CalculateToll(object vehicle) =>  
        vehicle switch  
    {  
        Car c           => 2.00m,  
        Taxi t          => 3.50m,  
        Bus b           => 5.00m,  
        DeliveryTruck t => 10.00m,  
        { }             => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)),  
        null            => throw new ArgumentNullException(nameof(vehicle))  
    };  
}  

2) what is the meaning of this line using toll_calculator;

all code taken from this url https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/tutorials/pattern-matching

thanks

Answer 1

Using top down style is harder to comprehend code so look at it from old school.

using System;
using Calculators;
using CommercialRegistration;
using ConsumerVehicleRegistration;
using LiveryRegistration;

namespace ConsumerVehicleRegistration
{
    partial class Program
    {
        static void Main(string[] args)
        {
            var tollCalc = new TollCalculator();
            Car car = new ();
            Console.WriteLine(tollCalc.CalculateToll(car));
            Console.ReadLine();
        }
    }
}

namespace Calculators
{
    public class TollCalculator
    {
        public decimal CalculateToll(object vehicle) =>
            vehicle switch
            {
                Car c => 2.00m,
                Taxi t => 3.50m,
                Bus b => 5.00m,
                DeliveryTruck t => 10.00m,
                { } => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)),
                _ => throw new ArgumentNullException(nameof(vehicle))
            };
    }
}
namespace ConsumerVehicleRegistration
{
    public class Car
    {
        public int Passengers { get; set; }
    }
}

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

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

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

Answer 2

1) the pattern match is using the type pattern match. often you want access a property of the type, you you can define an identifier which is types and passed to the match expression

var x = y switch  
{ 
    Car c => c. Passengers, 
    _ => 0 
}; 

this is not an assignment, if y is of type Car, return the value of Passengers. that is patten matching used with a switch or an if statements is an expression returning a value, not an assignment.

but in the sample code the identifier is not used, so a better version is:

  public decimal CalculateToll(object vehicle) => vehicle switch 
     { 
         Car            => 2.00m, 
         Taxi           => 3.50m, 
         Bus            => 5.00m, 
         DeliveryTruck  => 10.00m, 
         { }            => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)), 
         null           => throw new ArgumentNullException(nameof(vehicle)) 
     }; 

2) CalculateToll() is a regular function, written as a single line expression. C# allows

public bool DoNot1(bool x) 
{ 
    return !x; 
} 

public bool DoNot2(bool x) => !x; 

both these function work the same;

3) it a namespace. I believe it is a typo, I think they wanted:

using Calculators;