在C＃中是否可以访问仅具有属性值的类实例？

Question

May be it's silly question , but is it possible to realize such scenario? I have a class , eg

public class Car
{
public string Make {get;set;}
public string Model {get;set;}
public decimal Price {get;set;}
public User Owner {get;set;}
}

where owner is the property setting somewhere else and than i have a function

public static class Operations
    {
public static void CalculateTaxes(decimal price)
       {
           ....some code goes here and I want using reflection to access Owner,supposing that i will always pass price of a car
       }
    }

that function will be called like this

var car =new Car(){Price=25000,Make="BMW",Model="X6",Owner=new User(){"Sam Johnson"}};
Operations.CalculateTaxes(car.Price);

This is just a fake code, in real app I don't want to pass the whole instance , but want to get hold of the car owner.Is it a real goal ?

Answer 1

The answer to your question is simple and short: No. This is not possible, under any circumstance- because of how C# is designed. Thank Mads for that.

Imagine the security implications of passing an integer to a compromised 3rd party library- and accidentally leaking user credentials by doing so.

The real issue here is a design issue. Your code is not designed to suit the needs of your application. Rethink your design.

Also note that while reflection has many use cases and enables a lot of things, in such simple cases- it is usually overkill. Use reflection for meta programming - not for business logic.

Answer 2

Not only can that not be done with decimal which is a value type. Even a reference type such as a class won't work because (AFAIK) classes do not keep track of all of the objects that point to them (The same class instance can be a property of multiple owners).

Fortunately there's a simple solution - pass the car instance itself, and extract the price from it.

public static void CalculateTaxes(Car car)
{
    decimal price = car.Price;
    ...
}

If you need to call this method with types other than Car , you can create an appropriate interface and have Car implement it. Such as an interface with an Owner property. But since you're trying to get more properties of the car, I'm assuming this is going to be used only for type Car .

Answer 3

I thought of that solution ,but it's now what I want,as there will be a lot of properties of different type and each of them should be process in a different function and I want to pass them using dot notation ,not like CalculateTax(car,"Price")

I think , that the best solution will be to use local functions, which will have access to the whole object like

public static class Operations
    {
    public static void Operate(Car car)
       {
           calculateTaxes(car.Price);
         void calculateTaxes(decimal price)
         { 
          car.Owner is accessible here 
          }

         void rateMake(string make)
         { 
          so on and so on
          }


       }

    }