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Introduction to SOM

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Revision as of 19:46, 7 November 2004 by Prokushev (talk | contribs)

Introdution to SOM (System Object Model)

by Prokushev

System Object Model (SOM, SOMObjects) is a language neutral object model. Main advanage of SOM is possibility to implement classes in any language which supports DLL creation or usage. Only defined thing for such model is Interface. Interface described in terms of Interface Definition Language which can be translated to corresponding language binding. Classes represented in binary form (In language-specific object models classes exists only virtually until compilation. As example of such languages can be C++, Delphi, Pascal and other.). Actually, inherence implemented during runtime, like in true object-oriented languages like SmallTalk. Instanse of class represented by object. Actually, objects of same class shares same code. Code ca be stored either in DLL or in EXE. Most usable is DLL. DLL can contain one or more classes. DLL, in terms of SOM, named as classes library. Most of SOM functionality (except implementation of core logic) implemented with classes library.

By default with eComStation shiped lot of general classes library. One of then used every day and every minute, another - not so often. Later we will briefly look at all of them. Classes libraries includes:

Most notable classes (from users point of view) is Workplace Shell Classes. Desktop objects is SOM in work. Every day users uses SOM objects and most of them like it.

SOM objects can be manipulated easely. Using power of Object REXX and SOM users and programmers can do fantastic thing without any problems. WPS can be easely customized and manipulated with Object REXX.

Another powerfull set of classes is OpenDoc Classes. Not part of eComStation system they allows to have higly integrated and user-friendly applications. If programmer will support OpenDoc then we can have lot of good application (sick! No application term in OpenDoc word!). No monsters like Open Office or Lotus Smart Suite. No applications like GIMP. Only components which allows to build documents with very-very impressive content by easy operations. It is possible. It is future of OS/2 and eComStation. We can make our word better. So, in future, we'll try to review OpenDoc classes closer.

Don't forgot about DSOM classes - implementation of CORBA specification. Not latest, but we can move forward and extend DSOM classes to support most (or all) features of current CORBA specification. It is also possible. SOM is open model. Most of classes and methods can be easely extended or replaced.

Don't forgot about other object models also. Most notable is XPCOM. Mozilla users uses XPCOM every time. It's DOM support. XPCOM can be wrapped by SOM classes and reused by OS/2 programmers. It's anothe topic for future reviews.

Remember Java. Java classes and objects can be accessed via SOM. Mixing portable and native solutions allow us to have fantastic things. Native interface and cross-platform background. And vise versa.

We can do all of it, we must do all of it. We must learn such things as SOM. Really, things not so hard as we think.

Lets create our first SOM class. It is easy.

  • Step 1. Write interface
  • Step 2. Create binding
  • Step 3. Write class implementation
  • Step 4. Use class

Nothing hard. All too easy...

Write interface

Class interface must be described using Interface Definition Language. Some of developers uses only implementation language to describe class interface (sick!). Such approach ugly and incorrect. Doing so they closes it's classes for other. Use Interface Definition Language and nothing more. It's clear. It's easy. It's usefull.

#include <somcls.idl>
// include base classes

interface Demo : SOMObject
// Class Demo with parent SOMObject
{
 attribute string DemoWord;
 // Very-very usefull data
 void sayDemoWord();
 // Very-very usefull method
};

Is it hard? No!

Create bindings

In short, use SOM Compiler:

sc -s"h;ih;c" demo.idl

Result:

demo.h
demo.ih
demo.c

Is it hard? No!

Write class implementation

Ok. We have demo.c. Let's play the game:

/*
 *  This file was generated by the SOM Compiler and Emitter Framework.
 *  Generated using template emitter:
 *      SOM Emitter emitctm: 2.23.1.9
 */

#ifndef SOM_Module_demo_Source
#define SOM_Module_demo_Source
#endif
#define Demo_Class_Source

#include "demo.ih"


/*
 * Very-very usefull method
 */

SOM_Scope void  SOMLINK sayDemoWord(Demo *somSelf, Environment *ev)
{
    DemoData *somThis = DemoGetData(somSelf);
    DemoMethodDebug("Demo","sayDemoWord");

    printf("Write %s\n",_get_DemoWord(somSelf, ev));
}

Is it hard? No! Let's compile demo (don't forgot to chech include paths):

wcc386 demo.c

Use class

Is we need code which we can't use? No! Let's use it!

#include "demo.h"

int main(int argc, char *argv[])
{
  // Get environment info
  Environment *ev = somGetGlobalEnvironment();

  // Create demo1 and demo2 objects
  Demo *demo1 = DemoNew();
  Demo *demo2 = DemoNew();

  // Set DemoWord attribute of objects
  Demo__set_DemoWord(demo1, ev, "123");
  Demo__set_DemoWord(demo2, ev, "321");

  // Call sayDemoWord method of objects
  Demo_sayDemoWord(demo1, ev);
  Demo_sayDemoWord(demo2, ev);

  // Destroy objects
  _somFree(demo1);
  _somFree(demo2);

  // Finish
  return 0;
}

Is it hard? No! Let's create demo:

 wcc386 test.c
 wlink file demo.obj file test.obj library somtk.lib name test.exe

Run it! All must be Ok. It's easy.