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

EtreCheck 3.1.5 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
WALTR 2 2.0.8 - $39.95
WALTR 2 helps you wirelessly drag-and-drop any music, ringtones, videos, PDF, and ePub files onto your iPhone, iPad, or iPod without iTunes. It is the second major version of Softorino's critically-... Read more
Carbon Copy Cloner 4.1.12 - Easy-to-use...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
Dropbox 16.3.27 - Cloud backup and synch...
Dropbox is an application that creates a special Finder folder that automatically syncs online and between your computers. It allows you to both backup files and keep them up-to-date between systems... Read more
Microsoft OneNote 15.29 - Free digital n...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more
Spotify 1.0.44.100. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
SpamSieve 2.9.27 - Robust spam filter fo...
SpamSieve is a robust spam filter for major email clients that uses powerful Bayesian spam filtering. SpamSieve understands what your spam looks like in order to block it all, but also learns what... Read more
VueScan 9.5.62 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Fantastical 2.3.2 - Create calendar even...
Fantastical 2 is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event... Read more
PCalc 4.4.4 - Full-featured scientific c...
PCalc is a full-featured, scriptable scientific calculator with support for hexadecimal, octal, and binary calculations, as well as an RPN mode, programmable functions, and an extensive set of unit... Read more

Latest Forum Discussions

See All

Track Santa with these three festive app...
Christmas is fast approaching and that means it's time to prepare for Santa's yearly pilgrimage around the globe. Christmas Eve is an exciting time as parents help their kids get ready to welcome Santa. You've got the cookies and milk all planned... | Read more »
Galaxy on Fire 3 and four other fantasti...
Galaxy on Fire 3 - Manticore brings the series back for another round of daring space battles. It's familiar territory for folks who are familiar with the franchise. If you've beaten the game and are looking to broaden your horizons, might we... | Read more »
The best apps for your holiday gift exch...
What's that, you say? You still haven't started your holiday shopping? Don't beat yourself up over it -- a lot of people have been putting it off, too. It's become easier and easier to procrastinate gift shopping thanks to a number of apps that... | Read more »
Toca Hair Salon 3 (Education)
Toca Hair Salon 3 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Winter comes to Darkwood as Seekers Note...
MyTona, based in the chilly Siberian city of Yakutsk, has brought a little festive fun to its hidden object game Seekers Notes: Hidden Mystery. The Christmas update introduces some new inhabitants to players, and with them a chance to win plenty of... | Read more »
Bully: Anniversary Edition (Games)
Bully: Anniversary Edition 1.03.1 Device: iOS Universal Category: Games Price: $6.99, Version: 1.03.1 (iTunes) Description: *** PLEASE NOTE: This game is officially supported on the following devices: iPhone 5 and newer, iPod Touch... | Read more »
PINE GROVE (Games)
PINE GROVE 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: A pine grove where there are no footsteps of people due to continuous missing cases. The case is still unsolved and nothing has... | Read more »
Niantic teases new Pokémon announcement...
After rumors started swirling yesterday, it turns out there is an official Pokémon GO update on its way. We’ll find out what’s in store for us and our growing Pokémon collections tomorrow during the Starbucks event, but Niantic will be revealing... | Read more »
3 reasons why Nicki Minaj: The Empire is...
Nicki Minaj is as business-savvy as she is musically talented and she’s proved that by launching her own game. Designed by Glu, purveyors of other fine celebrity games like cult favorite Kim Kardashian: Hollywood, Nicki Minaj: The Empire launched... | Read more »
Clash of Clans is getting its own animat...
Riding on its unending wave of fame and success, Clash of Clans is getting an animated web series based on its Clash-A-Rama animated shorts.As opposed to the current shorts' 60 second run time, the new and improved Clash-A-Rama will be comprised of... | Read more »

Price Scanner via MacPrices.net

Never Settle for Low Performing Wifi With iOS...
AppYogi Software has announced the release of WiFi Signal Strength Status App 1.0, the company’s new utility developed exclusively for macOS. WiFi Signal Strength Status App features a unique, single... Read more
New 2016 13-inch Touch Bar MacBook Pros in st...
B&H Photo has stock of new 2016 Apple 13″ Touch Bar MacBook Pro models, each including free shipping plus NY sales tax only: - 13″ 2.9GHz/512GB Touch Bar MacBook Pro Space Gray: $1999 - 13″ 2.... Read more
New 2016 15″ Touch Bar MacBook Pros in stock...
B&H Photo has new 2016 Apple 15″ Touch Bar MacBook Pro models in stock today including free shipping plus NY sales tax only: - 15″ 2.7GHz Touch Bar MacBook Pro Space Gray: $2799 - 15″ 2.7GHz... Read more
DietSensor App Targeting Diabetes and Obesity...
DietSensor, Inc., a developer of smart food and nutrition applications designed to fight diabetes and obesity and help improve overall fitness, has announced the launch of its DietSensor app for... Read more
Holiday 2016 13-inch 2.0GHz MacBook Pro sales...
B&H has the non-Touch Bar 13″ MacBook Pros in stock today for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1449 $... Read more
Holiday sale: Apple TVs for $51-$40 off MSRP,...
Best Buy has dropped their price on the 64GB Apple TV to $159.99 including free shipping. That’s $40 off MSRP. 32GB Apple TVs are on sale right now for $98 on Sams Club’s online store. That’s $51 off... Read more
12-inch Retina MacBooks, Apple refurbished, n...
Apple has restocked a full line of Certified Refurbished 2016 12″ Retina MacBooks, now available for $200-$260 off MSRP. Refurbished 2015 models are available starting at $929. Apple will include a... Read more
Holiday sale: 12-inch Retina MacBook for $100...
B&H has 12″ Retina MacBooks on sale for $100 off MSRP as part of their Holiday sale. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1199 $100... Read more
Apple refurbished 13-inch MacBook Airs availa...
Apple has Certified Refurbished 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.6GHz/8GB/128GB MacBook Air: $849 $... Read more
Apple refurbished iMacs available for up to $...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
US- *Apple* Store Leader Program - Apple (Un...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
Automotive Detailer - *Apple* Used Autos -...
We are currently conductinginterviews and will be accepting applications for a part-time detailer. Apple Used Autos is a great place to work andstart a career. We Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- Trumbul...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.