From Lazarus wiki
Revision as of 13:09, 10 September 2014 by Thaddy (talk | contribs) (Example)



The Key Objects Library - a.k.a. KOL - is an object oriented framework created by Vladimir Kladov (http://kolmck.net) in 2000.
It is the successor to the XCL library by the same author.
The current release as of March 2014 is 3.22.
New versions appear with Irregular intervals, but the library is currently maintained.

The main reason creating this library is explained through the dissatisfaction of Vladimir and others towards ever increasing codebloat.
Nobody seemed to care anymore about *efficient* coding.
According to KOL users there a strong correlation between Moore's law and degrading code optimizing efficiency.

The framework centers around three basic concepts:

  • It uses - some say old school - pascal objects, not classes.
  • Most of the widgets are basically one and the same object. Polymorphism is through constructing functions.
  • It ignores the VCL/LCL, in fact it attempts to replace them.

This has several advantages, some of which are:

  • The size of your binary is very tiny, on average more 80% smaller than a VCL/LCL binary, but a factor 100 is not unusual.
  • KOL binaries (both executables and dll's) have much much faster load times and feel snappier.
  • KOL is very easy to extend once you understand its concepts. It is a fully object oriented framework

It also has very obvious disadvantages, some of which are:

  • KOL is a framework. It doesn't mix very well with classes and it can't be sensibly mixed with LCL/VCL code because you will loose the size advantage.
  • If you are not familiar with the old Object Pascal paradigm from Turbo Pascal the learning curve can be steep.
  • You will miss some functionality that has become common place, like RTTI, but most of these features are often codebloat and the reason why KOL exists in the first place.
  • Because you are often working on the same object with multiple appearances, it may be confusing that some methods or properties that you can see in the code editor do not apply.


  • Free Pascal compiler 2.6.4 or later for Win32
  • Free Pascal compiler 2.7.1 or later for Win64
  • KOL 3.22 or later for win32
  • The Mirror Classes Kit a.k.a. MCK for those who want to develop using a visual designer like Lazarus or Delphi.
  • Release preview of KOL 3.22-64 for KOL win32/64
  • See the KOL CE page for win-ce development and requirements.
  • Not required, but recommended is a copy of FPC's RTL and/or Delphi's RTL sources

Supported targets

  • All 32-bit Windows: from Windows 95 to Windows 8.1.
  • All 64-bit x86_64 from Windows 2000 to Windows 8.1.
  • Windows CE based PocketPC and Smartphones. More information on the KOL CE page


Let's illustrate KOL with a simple example. A form, a button and some action.
You will notice that the code resembles that of a LCL/VCL application and basically:
It does exactly the same!
The main difference is the use of objects and pointer to objects instead of classes and the use of constructing functions instead of constructors.

Here's the main program file:

 program koldemo;
 {This line makes us FPC and Delphi compatible}
  koldemo1 in 'koldemo1.pas';
  NewForm1( Form1, nil);

And here is the main unit, again, you will notice it is very similar to LC/VCL code:

 unit koldemo1;
   Windows, Messages, Kol;
  cps:KolString = 'Kol project in ' + {$IFDEF FPC}'Freepascal '{$ELSE}'Delphi '{$ENDIF} +
     {$IFDEF WIN64}'64 bits '{$ELSE}'32 bits '{$ENDIF} +
     {$IFDEF UNICODE_CTRLS}'Unicode'{$ELSE}'Ansi'{$ENDIF};
   Form, Button:pControl;{Note both widgets are of the same type}
   {The message handler for our Button}
   procedure ButtonClick(Sender:PObj); {The message handler for our Button}
 procedure NewForm1( var Result: PForm1; AParent: PControl );
 procedure NewForm1( var Result: PForm1; AParent: PControl );
   with Result^ do
     {The appearance of a widget depends on its creating function}
     Form := NewForm(AParent,cps);
     Button := NewButton(Form,'&Click Me');
     {Attach the MessageHandler}
     Button.OnClick := ButtonClick;
     { The applet variable is the Application object
       Assigning the main for to it assigns the main message loop to the form.}
 procedure TForm1.ButtonClick(Sender: PObj);

So what's so special about it?
Well, for one, compile this and look at the executable size.
A similar program, Form + Button + ShowMessage compiled with Delphi 7 is 394 Kilobytes and it gets worse for progressive newer versions of Delphi:2267 Kilobytes XE7-32, 3672 Kilobytes XE7-64
Compiled with Delphi 7 it renders an executable of 20 Kilobytes with Delphi 7 (36 XE7-32, 69 XE7-64). That is almost 20 times smaller than the same D7 VCL, 62 times smaller than XE7-32 VCL and 53 times smaller than XE7-64 VCL!
These numbers are relative to the respective compilers, i.e. KOL and VCL compiled with the same compiler.

Compiled with PPC386 it renders an executable of 48128 bytes. Compiled like:

ppc386 -Mdelphi -CX -XX -Xs -Os koldemo.dpr 

Compiled with PPCX64 for Windows it renders 65536 bytes. Compiled like:

ppcx64 -Mdelphi -Rintel -CX -XX -Xs -Os koldemo.dpr

The above examples are for an ANSI application. To compile a UNICODE application, simply add the UNICODE_CTRLS define, like:

ppcx64 -Mdelphi -Rintel -dUNICODE_CTRLS -CX -XX -Xs -Os

Note that especially for 64 bit, FreePascal renders consistently smaller code than its expensive cousin.
Also note that 32 bit FreePascal has a slightly bigger runtime payload than its cousin. The size difference disappears when you application is more complex.


For size, KOL defaults to an ugly system font. Here are multiple ways to remedy that:

 {Add this code after the NewForm Function}
 {Release the font}
 {Assign the default windows GUI font object}

The second method is slightly more involved, but is the |MSDN recommended way:

 {Add this function}
 function GetGuiFont:TLogFont;
 var Metrics:TNonClientMetrics;
   Metrics.cbSize := SizeOf(Metrics);
   SystemParametersInfo(SPI_GETNONCLIENTMETRICS, SizeOf(Metrics), @Metrics, 0);
   Result := Metrics.lfMessageFont;
 {And call it after the form creation}
 Form.Font.LogFontStruct :=GetGuiFont;

Fonts in KOL are objects of type TGraphicTool. This object can also represent pens and brushes.
We can also create a new GraphicTool object representing the GUI font:

 {The KOL way to assign the GUI font}
 function GuiFont:PGraphicTool;
 var Metrics:TNonClientMetrics;
   Result := NewFont;
   Metrics.cbSize := SizeOf(Metrics);
   SystemParametersInfo(SPI_GETNONCLIENTMETRICS, SizeOf(Metrics), @Metrics, 0);
   Result.LogFontStruct := Metrics.lfMessageFont;
 {We can now assign the new font to the Form's font property}

And this is the result: kolscreenshot.png