C#

// The base class
public class F1 : ... {
    ...
    System.Windows.Forms.Button button1 = new System.Windows.Form.Button();
    ...
    // Here is your standar .ctor
    public F1() {
       ...
       // Initialize the form in what ever wy you desire
       ...
    }
    // Here is the .ctor that hides the button
    public F1(bool hideButton) : this() {
       button1.Visible = hideButton;
    }
    ...
}

// The derived class
public class F2 : F1 {
   ...
   public F2 : base(true) {
      // initialize the form normaly
   }
   ...
}

// The base class
public class F1 : ... {
    ...
    System.Windows.Forms.Button button1 = new System.Windows.Form.Button();
    ...
    public SetButtonVisibility {
       get {
          return button1.Visible;
       } 
       set {
          button1.Visile = value;
       }
    }
    // Here is your standar .ctor
    public F1() {
       ...
       // Initialize the form in what ever wy you desire
       ...
    }
    ...
}

// The derived class
public class F2 : F1 {
   ...
   public F2 : base(true) {
      SetButtonVisibility = false;  // same as base.SetButtonVisibility = false;
      // initialize the form normaly
   }
   ...
}

public class MyClass : System.Windows.Forms.Form
{
    protected MyFormerlyAbstractClass functionality = new MyFormerlyAbstractClass();

    public void SomeMethod()
    {
        // Where you would have been able to call into a base method of MyAbstractClass
        // you can now do this:
        functionality.SomeMethodOnMyFormerlyAbstractClass();
    }
}

public void SomeInterfaceMethod()
{
    functionalty.SomeInterfaceMethod();
}

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"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucious

[FieldOffsetAttribute(4)]<br />
    public uint[] _private_data; // 64

[FieldOffsetAttribute(4), MarshalAs(UnmanagedType.ByValArray,SizeConst=64)]<br />
public uint[] _private_data; // 64

using System;
using System.Windows.Forms;

namespace WindowsApplication1
{
  public class MyTabControl : TabControl
  {
    private int lastSelectedIndex = 0;
    public MyTabControl() : base()
    {
      lastSelectedIndex = this.SelectedIndex;
      this.SelectedIndexChanged +=
        new EventHandler( SelectedIndexChanged );
    }

    private void SelectedIndexChanged( object sender, EventArgs e )
    {
      // Prevent someone from choosing TabPage number 3.
      if( this.SelectedIndex == 2 )
      {
        this.SelectedIndex = lastSelectedIndex;
      }
      else
      {
        lastSelectedIndex = this.SelectedIndex;
      }
    }
  }
}