TweetFollow Us on Twitter

July 93 - OOPC

OOPC

Gary Odom

OOPC is a full source code software development toolkit. OOPC has two components: an object system that turns standard C into a dynamic object-oriented programming language, and an application development framework to accelerate application development. This article tells why OOPC was created (its design goals), and in doing so provides a description of OOPC's feature set.

The Macintosh version of OOPC has been shipping since August, 1992, and is currently at version 1.3. A Windows version is going to be available before the end of 1993. OOPC's API (application programming interface) is already platform-independent.

Object System

OOPC's object system was designed to allow flexible object-oriented programming in C. The OOPC object system was created in 1988 for an artificial intelligence program. The specific design goals of OOPC's object system, all of which were achieved, were as follows.
  • Standard C syntax that works on any C compiler.
  • Multiple inheritance.
  • Dynamic definition of inheritance and method attachment, where classes and objects are completely defined (and can be modified) at run-time.
  • Fast execution speed.
  • Flexible usage of classes and objects: allowing a class to have its own data, separate from the objects it creates; and allowing object methods (separate from the class an object inherits from).
  • Enforce a simple API.
  • Provide dispatch control (before- and after-methods) that maximize code reusability.
  • Provide an abstraction mechanism for subsystem processing (which classes do not provide).
  • Garbage collection and support for object linkage (necessary for both garbage collection and OODB).
  • Provide support for collections, which are integral to OOP.

There is a common myth that an object system requires compiler support. Most object systems are implemented using a new language (such as Dylan), or an extension to an existing language (CLOS, C++), which require a new compiler (or at least a preprocessor), but this results from a design decision to create or modify existing language syntax, or simply to implement the object system using a compiler. People who design object systems are often computer language junkies and compiler writers; people who are biased to think in terms of "advances" in syntax, which require a new compiler. C++ is a perfect example of such tinkering. OOPC fully implements dynamic object-oriented programming without requiring special preprocessing or compiler implementation.

There is a trend in object-oriented programming products towards flashy development environments, with slinky linkers that slip patch code in without having to quit running an application in a debugging session, or other frilly features that "give great demo." That was never on the goal agenda for OOPC. OOPC is a simple-but-sophisticated, meat-and-potatoes code library. OOPC works with any C compiler. This approach keeps Electron Mining's development efforts focused on providing leverage for its customers, to accelerate their application development, not on spinning marketing flash (or trying to rope people into a proprietary development environment).

Most advanced object systems take their inspiration from CLOS, as does OOPC. CLOS provides dynamic definition of class-objects, and the use of generic functions to enforce a simple API.

OOPC uses verb functions, which are the same concept as CLOS's generic functions. (The term verb is used to emphasize the concept of verb-object action. Generic seemed too nondescriptive.) Any object is drawn using draw, or acted upon using act. Different verbs may dispatch to the same method. Often, the same method is used to draw or print an object; only a few classes have objects that print differently than they draw. Thus, using verb functions both simplifies the API and makes it consistent, and provides a means for greater code reuse while doing so. The verb set is extensible.

Before-methods and after-methods provide dispatch control, minimize dispatch overhead (by dispatching to two methods in a single call), and maximize code reuse (by allowing selective method overriding). OOPC also implements the concept of middle-methods, where dispatch can continue from inside a method (using continue_dispatch). Dispatch can also be targeted to a specific method (using dispatch_to).

OOPC dispatch is table driven, making it very fast. A verb is actually an index into a method table, masquerading as a function call. Methods can be defined or changed any time during program execution. Dynamic definition allows all aspects of object orientation to be defined and modified at run-time. The effect on flexibility with regard to design and implementation is profound.

A simple example of dynamic inheritance: while reading in a dialog item resource for a file, create dialog item objects, then add the right class (control, picture, text, and so on) to a dialog item once the item type is discovered (by reading the dialog item resource data). This can be done in a static OOP language by not assigning the dialog item type class before reading the dialog item resource definition, but that involves processing in a way dictated by the language's limitations, rather than doing things the way that might first come to mind (which is usually the most straight-forward way) if no constraints were imposed. The flexibility of a dynamic object system brings both small and large benefits.

Object orientation with OOPC is achieved using a small set of functions. new_class is used to create a class. new_object creates an object. define_method associates a verb function with a specific method. set_method_flag sets a before- or after-method status for a method.

OOPC implements the concept of agents. An agent is a subsystem of processing. There are agents for overall application processing (startup, quit), events handling, printing (page setup, print job, printing), cursor control, and menu/menu item enabling/disabling. An agent is associated with a class, but provides a mechanism to encapsulate processing and allow processing modification, much as a class encapsulates object data and behavior.

OOPC's object system has built-in support of object linkage. Objects can be linked to one another. This has two purposes. First, in a software world of self-contained modularity, object links are essential for object interaction. A tear-off menu, for example, is a cooperative effort between a menu, a window actor, a view, one or more lists, and a picture of the view (for rapid drawing of the view for the menu). Having an object system that has object linkage support built in facilitates setting up component software interaction. Second, object links are used for garbage collection; specifically, to make sure an object isn't freed if any other objects are using it.

Maintaining collections is an essential aspect of object-oriented programming. A document is a collection of pages. A view is a collection of objects that appear in the view. A menu bar is a collection of menus, each of which is a collection of menu items. The OOPC object system has efficient functions for maintaining collections.

Application Framework

The design goals of the application framework were as follows.
  • A streamlined class library architecture for simplified learning and maintenance.
  • Full user interface feature set.
  • Simple but sophisticated rule-based activity control.
  • Automatic document management.
  • Data management.
  • Built-in object persistence that can be applied to new classes with little or no additional code.
  • Multiple-priority event processing, include threading.
  • Accelerated memory management optimized for a large number of blocks.
  • Comprehensive, sophisticated exception handling.
  • Good debugging tools.
  • Object-oriented graphics package.
  • A universal language styled text engine.
  • Platform independence.

The architecture of the OOPC class library revolves around actors. A document is a type of actor, as are dialogs. Actors are at the top of the activity hierarchy. Actors handle window events, because actor objects own window objects.

What happens when a user clicks on an object within the content region of a window? The EventAgent tells the actor that an event has occurred in the window owned by it. The EventAgent calls the actor to act. The actor looks to its window, which holds the window's view(s). A view holds a collection of objects that are visible in the window. Windows have at least one view. The actor looks through the objects in its view(s) until it finds the object sitting where the mouse was clicked, then calls that object to act upon itself.

An actor manages its window and the objects that appear in the window. Visually, an actor controls window display. A window draws the views in itself. Each view draws the objects in itself. A document uses the concept of pages. Each page manages display of its own view in the document window. A document manages pages, and adds a new object to itself by adding it to its current page.

MacApp, which is view-happy, requires that every object in a view belongs to a view subclass. OOPC suffers no such architectural nonsense. An OOPC view is simply a container for a collection of objects that has its own coordinate system. Views can be selected for onscreen or offscreen drawing (if the view has an offscreen bitmap).

OOPC 1.3 has three document classes, all of which handle multiple-page documents. cDocument handles documents where the pages appear one after another vertically, as with a word processor. cPoster provides a large, poster-sized document, such as those used in drawing programs. cRecordDoc implements the database record model, where only one page/record is visible at a time. There is also a list actor class that can be put into use for spreadsheet documents. Acting, drawing, printing, undo and scrap operations are handled automatically.

OOPC's class library provides a full set of user interface features. In addition to the classes you would expect, tear-off menus, floating windows, tool, pattern and color palette classes are also provided. All modal dialogs are automatically movable modals, even under System 6. User interaction with standard dialog item types (controls, editable text) is handled automatically. OOPC provides a MultiFinder/System 7 type DA menu bar for any user running under the System 6 Finder.

OOPC controls are platform-independent. New control types can be easily implemented, requiring only a draw method override for simple controls, and an act method for more complex control types.

There is a rule class, used for activity control, and appropriate for building rule-based systems. Cursor and menu activation are controlled using rule objects. Rules can be merged using AND or OR joins to build a rule framework object.

OOPC has a sophisticated multiple-priority event processing agent. There are multiple event queues, each at a different priority. The OS event queue is a mid-priority queue. Handling for any type of operating system event can be modified with a single call to an EventAgent modifier. There is a timer event queue for periodic events. The number of event queues is extensible (by adding one or more constant definitions in the event header file). Threaded processing is accomplished by creating new events of the needed priority. Events can be controlled in any event queue, including operating system events.

OOPC has its own pointer-based memory management system. Figure 1 shows the results of timing studies on Mac OS and OOPC memory management. Large blocks are taken from the operating system and cut into smaller slices, which are for object-related data storage. The Jan/Feb 93 FrameWorks has an article detailing OOPC memory management.

OOPC has a simple exception handling mechanism that is used throughout the class library. Normal execution code is placed between CODE and HANDLER macro statements. Exception handling code, which cleans up by deallocating memory allocated during normal execution (and optionally sets an alert message), is located between HANDLER and CONTINUE_HANDLER statements. (CODE {normal execution code} HANDLER {exception handling code} CONTINUE_HANDLER). CONTINUE_HANDLER sends program execution up the stack frame to the calling method, so clean-up can occur through the call chain. END_HANDLER, which can be used instead of CONTINUE_HANDLER, terminates the jumping up the stack frame (thereby terminating the exception handling process). Exception handlers can be nested.

Error reporting is automatic. A variety of error reporting alerts are provided. The application agent reports errors during initialization, and the event agent reports errors while handling events. (The event agent manages all event handling, so is at the top of the call chain while an application is running.)

OOPC 1.3 comes with a fully interactive class browser and object inspector. Figure 2 shows the browser. Any data area that shows a class, object, or array of objects or methods is an active field that can be clicked on to bring up an inspector window.

The class browser is helpful in both learning OOPC, and for debugging. OOPC also has another valuable debugging tool: execution trace debug files which can be created during a debugging session at the switch of a compile option. A wrong or out-of-order processing call is a common cause of problems with object-oriented programming. An execution trace file is extremely helpful in fixing such a problem. Also, class methods consistently use data checking with exception handling to minimize the introduction of bugs during development and facilitate rapid debugging.

For data management, OOPC provides a variety of collection, array and list classes. There are classes for unordered collections, queues and stacks. There are bit array and variable-sized data array classes. OOPC has a list class that supports variable-sized rows and columns. The class browser shown in Figure 2 uses a subclass of the basic list actor class.

OOPC includes both paint and graphic object classes. Pictures, icons, and a full complement of geometric shapes are provided.

A text engine is currently under development. OOPC currently has a styled text class that uses the Macintosh Toolbox TextEdit. The next major version of OOPC will sport a powerful text engine that fits the bill for platform-independence. Along with the text engine will come a cTextDoc class that handles text editor document operations.

OOPC's API is already platform-independent. The release of OOPC for Windows in late 1993 will be proof of the pudding.

Conclusion

OOPC's object system was designed to yield maximum object-oriented flexibility and power using standard C, and enforce a simple, consistent API. OOPC's application framework was created to provide extensive support for accelerating development for a wide range of application types and needs. Four years old and already a mature product, OOPC class library development is ongoing in an effort to broaden its scope, providing further acceleration for application developers.
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Logic Pro X 10.1.1 - Music creation and...
Apple Logic Pro X is the most advanced version of Logic ever. Sophisticated new tools for professional songwriting, editing, and mixing are built around a modern interface that's designed to get... Read more
VLC Media Player 2.2.0 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Sound Studio 4.7.8 - Robust audio record...
Sound Studio lets you easily record and professionally edit audio on your Mac. Easily rip vinyls and digitize cassette tapes, or record lectures and voice memos. Prepare for live shows with live... Read more
LibreOffice 4.4.1.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
Freeway Pro 7.0.3 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
Cloud 3.3.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
Cyberduck 4.6.5 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more
Firefox 36.0 - Fast, safe Web browser. (...
Firefox for Mac offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and... Read more
Thunderbird 31.5.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
VOX 2.4 - Music player that supports man...
VoxIt just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features & support for all audio formats you should ever need... Read more

Get The Whole Story – Lone Wolf Complete...
Get The Whole Story – Lone Wolf Complete is Now Available and On Sale Posted by Jessica Fisher on February 27th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Who Wore it Best? The Counting Dead vs....
Like it or not, the “clicker” genre, popularized by cute distractions like Candy Box and Cookie Clicker, seems like it’s here to stay. So Who Wore it Best? takes a look at two recent examples: The Counting Dead and AdVenture Capitalist. | Read more »
Card Crawl, the Mini Deck Building Game,...
Card Crawl, the Mini Deck Building Game, is Coming Soon Posted by Jessica Fisher on February 27th, 2015 [ permalink ] Tinytouchtales and Mexer have announced their new game, | Read more »
Witness an all new puzzle mechanic in Bl...
Well, BlastBall MAX is not one of those games and is bucking trends such as timers, elements of randomness, and tacked-on mechanics in favor of pure puzzle gameplay. When you first boot up the game you’ll see a grid made up of squares that are each... | Read more »
This Princess Has a Dragon and She isn’t...
This Princess Has a Dragon and She isn’t Afraid to Useit. | Read more »
Mecha Showdown Review
Mecha Showdown Review By Lee Hamlet on February 27th, 2015 Our Rating: :: IN A SPINUniversal App - Designed for iPhone and iPad Mecha Showdown replaces traditional buttons with a slot machine mechanic in this robot fighting game,... | Read more »
Reliance Games and Dreamworks Unveil Rea...
Reliance Games and Dreamworks Unveil Real Steel Champions Posted by Ellis Spice on February 27th, 2015 [ permalink ] Reliance Games and Dreamworks have announced that a third game in | Read more »
Sum Idea Review
Sum Idea Review By Jennifer Allen on February 27th, 2015 Our Rating: :: TAXING NUMBERSUniversal App - Designed for iPhone and iPad Sum Idea is a fairly charming but taxing puzzle game.   | Read more »
A New Badland Update Brings Daydream Lev...
A New Badland Update Brings Daydream Levels to Co-Op Posted by Ellis Spice on February 27th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Slashing Demons Review
Slashing Demons Review By Lee Hamlet on February 27th, 2015 Our Rating: :: IT'S A LONG WAY TO THE TOPUniversal App - Designed for iPhone and iPad Slashing Demons lacks the depth or scope to take it beyond the point of being just... | Read more »

Price Scanner via MacPrices.net

Apple CEO Tim Cook to Deliver 2015 George Was...
Apple CEO Tim Cook will deliver the George Washington University’s Commencement address to GWU grads on May 17, at which time he will also be awarded an honorary doctorate of public service from the... Read more
Apple restocks refurbished Mac minis for up t...
The Apple Store has restocked Apple Certified Refurbished 2014 Mac minis, with models available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz... Read more
Save up to $50 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549 $50 off - 128GB iPad Air 2... Read more
16GB iPad Air 2 on sale for $447, save $52
Walmart has the 16GB iPad Air 2 WiFi on sale for $446.99 on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale price for online orders only,... Read more
iMacs on sale for up to $205 off MSRP
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1029 $70 off - 21″ 2.7GHz iMac: $1199 $100 off - 21″ 2.9GHz... Read more
Apple Takes 89 Percent Share of Global Smartp...
According to the latest research from Strategy Analytics, global smartphone operating profit reached US$21 billion in Q4 2014. The Android operating system captured a record-low 11 percent global... Read more
New Travel Health App “My Travel Health” iOS...
Rochester, Minnesota based Travel Health and Wellness LLC has announced that its new iOS app help safeguard the user’s health when traveling abroad — “My Travel Health” is now available on the Apple... Read more
Sale! MacBook Airs for up to $115 off MSRP
B&H Photo has MacBook Airs on sale for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $799 100 off MSRP - 11″ 256GB MacBook Air: $999 $100... Read more
15-inch 2.0GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished previous-generation 15″ 2.0GHz Retina MacBook Pros available for $1489 including free shipping plus Apple’s standard one-year warranty. Their price is... Read more
Wither The iPad mini? End Of The Road Imminen...
AppleDailyReport’s Dennis Sellers predicts that the iPad mini is going to be left to wither on the vine, as it were, and then just allowed to fade away — a casualty of the IPhone 6 Plus and other... Read more

Jobs Board

Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.