Overriding properties in c#-CodePudding

I have a question about overriding properties in c#. There already is a similar question here, but the answers are not satisfying for me. Let's say I have incoming classees:

 class A
{
    public int Prop { get; }
}

class B : A
{
    public int Prop { get; set;  }
}

Now as you can see I want to add a setter to the property Prop in a subclass. I came up with two solutions. The first one is making the peoperty virtual and override it in class B like this:

class A
{
    public virtual int Prop { get; }
}

class B : A
{
    public override int Prop { get; set;  }
}

But unfortunetaly the compiler doesn't allow me to do this. My second idea was to use a 'new' key word:

class A
{
    public virtual int Prop { get; }
}

class B : A
{
    public new int Prop { get; set;  }
}

Now everything seemingly works, but it's not a satysfying solution for me becuase of one detail. Let's consider for instance this piece of code:

B b = new B();
b.Prop = 5;
A a = b;
Console.WriteLine(a.Prop);

You probably know that I get 0 here in my output, but I want to get 5. Is there any way to solve this problem?

CodePudding user response：

A is not a subclass of B, this is not how inheritance works. I don't understand why do you want to do this, I think you are mistaken the complete concept of inheritance

In the case you proposes:

 class A
{
    public int Prop { get; }
}

class B : A
{
    public int Prop { get; set;  }
}

they are the same property. If you do a:

 class A
{
    public int Prop { get; }
}

class B : A
{
    public int AnotherProp { get; set;  }
}

you can set:

B instance = new B();
B.Prop = 5;

If what you want to do is having a property in a subclass with the same name (not recommended) you can do this, without working with inheritance:

internal class A
{
    internal int Prop { get; }
}

internal class B 
{
    internal A MySubClass { get; set;  }
}

B instanceB = new B();
A instanceA = new A();
instanceA.Prop = 5;
B.MySubClass = instanceA;

or you can play with that, without copy it directly. Is just an example to show you the difference between class as property and inheritance

CodePudding user response：

Propertie's setter in class A should be protected. You will still be able to override it and it still won't be accessible outside class A and its children.

CodePudding user response：

You could try to explicitly implement property's setter. This requires an interface:

public interface IPropSet
{
    int Prop { set; }
}

class A
{
    public int Prop { get; }
}

class B : A, IPropSet
{
    int IPropSet.Prop { set { } }
}

But unfortunately this property cannot be set without casting to IPropSet:

((IPropSet)new B()).Prop = 1;

CodePudding user response：

On Console.WriteLine(a.Prop); you reference to A.Prop, new in B class for Prop is for redefining.

When used as a declaration modifier, the new keyword explicitly hides a member that is inherited from a base class. When you hide an inherited member, the derived version of the member replaces the base class version. This assumes that the base class version of the member is visible, as it would already be hidden if it were marked as private or, in some cases, internal. Although you can hide public or protected members without using the new modifier, you get a compiler warning. If you use new to explicitly hide a member, it suppresses this warning.

but you can use,
if (a is B bb)
{
    Console.WriteLine(bb.Prop);
}
Or use this pattern
class A
{
    public virtual int Prop { get; protected set; }
}
class B : A
{
     public void SetProp(int prop) => Prop = prop;
}


B b = new B();
b.SetProp(5);
A a = b;
Console.WriteLine(a.Prop);