Override get, But not set

Question

I have an abstract class that defines a get, but not set, because as far as that abstract class is concerned, it needs only a get.

Answer 1

The reason that this is not possible is due to the way parameters are "Magicked" into existence by C#. When you define a parameter, C# creates a private field that the implicit getter and setter manipulate. If there is no setter in the base class, it's impossible to change this variable from a method written in a sub class (as the private flag prohibits even sub classes from accessing it). What usually happens is it uses the implicit setter of the base class instead.

I wouldn't advise putting the set in the base class if not all sub classes can do it, because this goes against the whole principle of polymorphic programming (any abstract method defined in the abstract class must be implemented by a subclass). Creating a special setter method, as described in other answers is probably the best way go.

Answer 2

If BaseClass is in your own codebase, then you can do:

abstract public class BaseClass
{
    abstract public double MyPop { get; protected set; }
}

public class DClass : BaseClass
{
    private double _myProp;
    public override double MyProp
    {
        get { return _myProp; }
        protected set { _myProp = value; }
    }
}

EDIT: You can then go make a public method in DClass SetMyProp(double myProp) or the like. The class design for your domain model should be clear about or speak for itself why you can't set the property directly in the base class and why you can do so in the derived one.

Answer 3

Siege

abstract class TestBase
{
    public abstract int Int { get; }
}

class TestDerivedHelper : TestBase
{
    private int _Int;
    public override int Int
    {
        get
        {
            return _Int;
        }
    }

    protected void SetInt(int value)
    {
        this._Int = value;
    }
}

class TestDerived : TestDerivedHelper
{
    public new int Int
    {
        get { return base.Int; }
        set { base.SetInt(value); }
    }
}

Using TestDerived will have the functionality you're looking for. The only drawback I can see from this method is that you have to implement every abstract method in TestDerivedHelper, but it gives you more control later.

I use this approach and works very well for me. Also, I made my "TestDerivedHelper" class abstract too, then all the methods must be implemented on "TestDerived" class.

Answer 4

You cannot override the set accessor since the base class has no set accessor defined.

What you can do is use the new keyword to hide the base classes implementation, but that may not be what you want.

Answer 5

public abstract class BaseClass
{
    public abstract double MyPop { get; }
}

public class DClass: BaseClass
{
    private double _myPop = 0;
    public override double MyPop 
    {
        get { return _myPop; }
    }

    // some other methods here that use the _myPop field
}

If you need to set the property from outside DClass then maybe it would be better to put the setter into the base class.

Answer 6

EDIT:

OK I may have been hasty with this response, but I've given it some more thought now.

Do you have to use an abstract base class? If it's not required, try this:

public interface ISomeRelevantName
{
    double MyPop { get; }
}

public class DClass : ISomeRelevantName
{
    public double MyPop { get; set; }
}