C＃/ C ++中的Builder设计模式是否需要提升的访问修饰符？

Question

Let's say we have a Vehicle class containing a private collection of wheels, and a method AddWheel(Wheel i_WheelToAdd). without using a builder pattern, I would want this method to be protected, but because I am using the builder design pattern, I have no choice but to set it to internal (to allow the builder to add wheels).

what is the correct object-oriented way to fix this issue?

(the use of a nested class doesn't help me in C#/C++, assuming inside Vehicle I have a nested class 'VehicleBuilder', this doesn't give it the ability to access a private/protected member of the parent like in java)

Answer 1

What I would do is have the Vehicle class take the builder as a constructor parameter and be responsible for ingesting all the settings created on the builder. I think of the builder as building all the parameters needed and getting the appropriate object back, it does not have to actually have to handle setting the properties directly. That way you can put the AddWheel on the builder and keep the Vehicle buttoned down.

public class Vehicle{
    public List<Wheel> Wheels {get; private set;}
    internal Vehicle(VehicleBuilder builder)
    {
         Wheels = builder.Wheels;
         //Set other useful properties...
    }
}

public class VehicleBuilder()
{
    private List<Wheel> _wheels = new List<Wheel>;
    internal List<Wheel> Wheels
    {
      get{return _wheels;}
    }
    public void AddWheel(Wheel wheelToAdd)
    {
        _wheels.Add(wheelToAdd);
    }
   public Vehicle GetVehicle()
   {
      return new Vehicle(this);
   }
}

Answer 2

One way is to make the builder as an inner class that gets exposed from the object itself:

class Vehicle
{
  ⁞
  class VehicleBuilder
  {
    ⁞
  }
  private Vehicle(...) { ... }
  public VehicleBuilder New => new VehicleBuilder();
}