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

Parallels Desktop 13.2.0 - Run Windows a...
Parallels allows you to run Windows and Mac applications side by side. Choose your view to make Windows invisible while still using its applications, or keep the familiar Windows background and... Read more
jAlbum Pro 15.0 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more
iFinance 4.3.4 - Comprehensively manage...
iFinance allows you to keep track of your income and spending -- from your lunchbreak coffee to your new car -- in the most convenient and fastest way. Clearly arranged transaction lists of all your... Read more
VueScan 9.5.92 - 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
Scrivener 3.0 - Project management and w...
Scrivener is a project management and writing tool for writers of all kinds that stays with you from that first unformed idea all the way through to the first - or even final - draft. Outline and... Read more
SuperDuper! 3.0.1 - Advanced disk clonin...
SuperDuper! is an advanced, yet easy to use disk copying program. It can, of course, make a straight copy, or "clone" -- useful when you want to move all your data from one machine to another, or do... Read more
jAlbum 15.0 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results - Simply drag and drop photos into groups, choose a design... Read more
Scrivener 3.0 - Project management and w...
Scrivener is a project management and writing tool for writers of all kinds that stays with you from that first unformed idea all the way through to the first - or even final - draft. Outline and... Read more
SuperDuper! 3.0.1 - Advanced disk clonin...
SuperDuper! is an advanced, yet easy to use disk copying program. It can, of course, make a straight copy, or "clone" -- useful when you want to move all your data from one machine to another, or do... Read more
Parallels Desktop 13.2.0 - Run Windows a...
Parallels allows you to run Windows and Mac applications side by side. Choose your view to make Windows invisible while still using its applications, or keep the familiar Windows background and... Read more

Latest Forum Discussions

See All

The mobile gamer's guide to Black F...
We're starting to catch wind of some exciting deals in the mobile gaming space for Black Friday. There are big discounts on mobile phones and accessories cropping up already, so you might want to get a move on things ahead of the big day. It's... | Read more »
The best pre-Black Friday deals - Novemb...
Black Friday will soon be upon us, but online retailers are already getting a headstart on the steep discounts. Don't wait until Friday—you'll find some pretty good deals all over the internet without waiting in lines or competing with other... | Read more »
Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »
A Boy and His Blob (Games)
A Boy and His Blob 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Fight terrible monsters and collect epic...
Released on Western markets early last month, Dragon Project, created by Japanese developer COLOPL, brings epic monster hunting action to mobile for the very first time. Collect a huge array of weapons and armor, and join up with friends to fight... | Read more »
I Am The Hero (Games)
I Am The Hero 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: I Am The Hero is a pixel art, beat 'em up, fighting game that tells the story of a "Hero" with a glorious but mysterious past.... | Read more »
Kauldron (Music)
Kauldron 1.0 Device: iOS Universal Category: Music Price: $3.99, Version: 1.0 (iTunes) Description: Kauldron is our warmest sounding, punchiest synth yet! A completely new modeling technology, combined with carefully designed... | Read more »

Price Scanner via MacPrices.net

Save up to $180 with Apple Certified Refurbis...
Apple has Certified Refurbished 2017 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.8GHz/8GB/128GB MacBook Air (... Read more
Black Friday deals on Apple Macs now live at...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP for Black Friday week. Shipping is free. Note that stock of some Macs may come and go during the week, so... Read more
Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more
Best Apple iPad deals this weekend, up to $80...
Apple resellers are offering 9.7″ iPads and 10.5″ iPad Pros for up to $80 off MSRP this weekend as part of their early Holiday and Black Friday sales: Adorama is offering new 2017 9.7″ 32GB WiFi... Read more
Early Black Friday sale: Apple iMacs for up t...
B&H Photo has 27-inch iMacs in stock and on sale for up $130-$150 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2149 $150 off... Read more
Apple restocks refurbished Mac minis starting...
Apple has restocked Certified Refurbished Mac minis starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: – 1.4GHz Mac mini: $419 $80 off MSRP – 2.6GHz Mac... Read more
Save on 12″ MacBooks, Apple refurbished model...
Apple has Certified Refurbished 2017 12″ Retina MacBooks available for $200-$240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free.... Read more
Early Holiday sale: 12″ iPad Pros for up to $...
B&H Photo has 12″ iPad Pros on sale today for up to $130 off MSRP. Shipping is free, and B&H collects no sales tax outside NY & NJ: – 12″ 64GB WiFi iPad Pro: $749, save $50 – 12″ 256GB... Read more
Holiday sale prices on Apple 13″ MacBook Pros...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for $100-$150 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro... Read more
Sale: 13″ MacBook Airs starting at $899, $100...
B&H Photo has 2017 13″ MacBook Airs on sale today for $100 off MSRP including free shipping. B&H charges NY & NJ sales tax only: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $100 off... 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
Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Pro/Consumer Apps Support Engineer -...
…exemplify AppleCare's expert technical support paired with exceptional customer service for Apple 's software apps. This person is a problem solver, who understands Read more
Partner Marketing Manager, *Apple* Pay - Ap...
Job Summary The Apple Pay partner marketing team is looking for a Marketing Manager to develop and drive US programs. The right candidate will be passionate about Read more
*Apple* Solution Consultant - Apple (United...
# Apple Solution Consultant - Rochester, MN Job Number: 113037950 Rochester, MN, Minnesota, United States Posted: 19-Sep-2017 Weekly Hours: 40.00 **Job Summary** Are Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.