TweetFollow Us on Twitter

September 90 - Meta-spaghetti

Meta-spaghetti

Donald E. Carlile

(BILL: I FORGOT TO GET A COMPANY NAME FROM DON. WANT TO GIVE IT A SHOP?)

I'm a fairly conscientious programmer-I like to think I write good clean code; I take the trouble to use modular techniques; I even stood on my head to learn object-oriented techniques. But in spite of all this, I found out I was writing spaghetti.

Spaghetti code! Someone still uses GOTO!?

Well, possibly I exagerrate: I don't mean spaghetti code in the old BASIC GOTO sense-```I mean spaghetti code that is only possible when you are writing in an OOP language. Maybe we'd better call it meta-spaghetti.

I found I was writing meta-spaghetti when I was asked by someone if I would let him use some of my objects. I had known I had only one unit, but I hadn't realized how tangled it was. It was then that I developed the term meta-spaghetti to define the condition of my code.

What I mean by meta-spaghetti is objects which refer to each other recursively. That is, objects which in their definitions include fields of each other's type, as in

TMyDocument = OBJECT(TDocument)
	
	fStar : TStar;
	…

	TStar = OBJECT(TObject)

		fMyDocument : TMyDocument;
	…

This leads to strange loops and to units which cannot easily be decomposed into simpler entities.

As anyone who has read even part of Hofstader's Gödel, Escher, Bach knows, it is impossible to entirely banish strange loops: you made that reference in the object definition for some reason, and it cannot be easily abandoned without some thought and work. That being said, you might still want to introduce some measure of isolation between your objects.

I can tell you from experience that it is difficult to undo the damage once it's done. As I was unraveling my code, however, I developed some guidelines for avoiding and dealing with meta-spaghetti. Perhaps they will prove helpful to you as well, as you design your code from the beginning to avoid this condition.

1. References should only to be to objects down the ownership chain.

As I was defining my set of rules, this is the first one that became apparent: when defining an object, references can be made to the internals of the objects it owns. This is what I mean by references down the ownership chain. (For a more complete discussion of the ownership chain, see the author's Chains Required, Whips Optional, an unpublished, and indeed unwritten, article.)

As an example, in my Trek-style game I had a method to add text to a textedit window. This method belonged to my document object. In order for my ship objects to add text about their status to the window, they had to have a reference to my document object. This caused a problem when I wanted my ship objects in a separate unit so that others could use them.

I solved this problem by changing the way I added text to the window. Instead of calling the document method, I added a text handle field to the ship object. I then changed my document DoIdle to check the texthandle of each ship object. In this way I followed the rule of having only references down the ownership chain.

If this rule is followed, the separation of objects into units becomes very clear and simple. There is no confusing interdependence of objects, and it is clear what the unit dependencies should be.

There is only one problem with this rule: it's not always possible or desirable to follow it. Some objects need to be interrelated; when this is the case, they probably should not be separated. This brings us to the next rule:

2. When it is impossible to remove references between objects, include them in the same unit.

The universe of my game is defined by two object types, TGalaxy and TQuadrant. These two object types refer to each other quite a lot, and it makes a great deal of sense for them to both be in the same unit. It is also unlikely that they would need to be separated to be reused. Therefore, I have put them into their own unit.

3. When it is impossible to untangle references and they must be in separate units, define a new object to make the references and push it down the ownership chain.

Don't be afraid to revise your structure. Although it will save you work to think out your structure ahead of time, sometimes this proves impossible. When you find you have painted yourself into a corner, cut a new doorway.

In my original design, my TMyDocument object owned all the lists of quadrants and other data containers. Thus, all my data objects referred back to it in order to refer to each other. When I wanted to separate out my ships, stars and quadrants into other units to make them usable elsewhere and to decrease compile time, I found the task impossible.

I then defined a new object, a TGalaxy, to contain all the objectionable fields and methods (no pun intended) and made a new field in the revised TMyDocument object to refer to an instantiation of TGalaxy. This made it possible to cleanly make the separation.

Make vanilla references when Rule 1 is impossible.

Another strategy for avoiding meta-spaghetti is to make references to the parent type rather than the type that is giving you trouble. This is not always possible, but sometimes the method or field you need to reference is contained in the object's parent or ancestor.

In my game, I call the draw method of my TQuadView object type from one of the methods of TQuadrant. I do this to avoid the flicker introduced when I use the invalid rectangle methods of MacApp. Originally TQuadrant included a field fMyDocument of type TMyDocument. TMyDocument, of course, had a reference to an fQuadView, of type TQuadView. TQuadView was a specialized descendant of TView. When I needed to do a drawing, I called fMyDocument.fQuadView.Draw. In this way, TQuadrant absolutely needed to be in the same unit as TQuadView. It was also specifically geared to my application only.

To untangle this particular mess, I added a field fQuadView, of type TView, to my TGalaxy object. Since variables of an ancestor type can contain any descendent, this field can contain an object of the specialized type TQuadView. The only limitation is that specialized fields and methods may not be called using this reference.

At the time an object of type TQuadView is made, it is passed to fGalaxy of the TMyDocument. Then I can call Draw, since Draw is one of the methods of the ancestor TView class.

5. Define proto-objects for objects up the chain when Rule 1 is impossible.

Sometimes all the above rules fail: you still want to break up objects into different units but they can't come completely apart. When this happens, it is important to remember that it is permissible to define objects or abstract classes which have no instantiation. You can define these "proto-objects" to contain those fields and methods which are necessary for the objects lower down the ownership chain and can include these classes in the same unit with those objects. Then USE that unit in the unit which defines the real objects and make them descendants.

As I mentioned earlier, TGalaxy and TQuadrant define the universe of my game. I found it impossible to completely divorce these objects from the objects I refer to, i.e., my ships, stars, bases,and torpedoes. I reasoned further that any structure which made use of my entities would also need some kind of quadrant and galaxy. I then defined a TProtoGalaxy and TProtoQuadrant, which had references for the fields and methods necessary for my entity unit, while not burdening the unit with the heavy details and the bulk of the fields and methods. I then defined TGalaxy as a descendant of TProtoGalaxy and TQuadrant as a descendant of TProtoQuadrant.

This one might be just a bit tricky to follow. Let me try and restate it thusly: the Galaxy and Quadrant objects have several fields and methods which ships and things need to reference. Two examples of such fields are the galaxy array and the list of other entities in the quad. An example of a referenced method is the one which detects when collisions occur. I therefore defined objects, which I call proto-objects, which contain references to these things. I don't define the methods-e.g., the collision procedure in the protoQuad consists of a Begin and an End, as do the rest of the methods in my proto-objects. In a different unit I then create descendants of the proto-objects with all the fields and fleshed-out methods fully defined.

I don't claim that these rules are the simple once-and-for-all solution to the problem of meta-spaghetti, but they are a start. You can probably come up with a few rules and methods of your own. Good luck!

Rules for avoiding meta-spaghetti:

  1. References should only to be to objects down the ownership chain.
  2. When it is impossible to remove references between objects, include them in the same unit.
  3. When it is impossible to untangle references, and they must be in separate units, feel free to define a new object.
  4. Make vanilla references when Rule 1 is impossible.
  5. Define proto-objects for objects up the chain when Rule 1 is impossible.

If you have any questions or comments for Don, he can be reached on AppleLink at N0231.

 
AAPL
$567.20
Apple Inc.
+42.45
MSFT
$39.44
Microsoft Corpora
-0.25
GOOG
$526.85
Google Inc.
-0.09

MacTech Search:
Community Search:

Software Updates via MacUpdate

Cyberduck 4.4.4 - 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
TechTool Pro 7.0.3 - Hard drive and syst...
TechTool Pro is now 7, and this is the most advanced version of the acclaimed Macintosh troubleshooting utility created in its 20-year history. Micromat has redeveloped TechTool Pro 7 to be fully 64... Read more
MacFamilyTree 7.1.6 - Create and explore...
MacFamilyTree gives genealogy a facelift: it's modern, interactive, incredibly fast, and easy to use. We're convinced that generations of chroniclers would have loved to trade in their genealogy... Read more
EtreCheck 1.9.9 - For troubleshooting yo...
EtreCheck is a simple little app to display 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... Read more
TeamViewer 9.0.28116 - Establish remote...
TeamViewer gives you remote control of any computer or Mac over the Internet within seconds, or can be used for online meetings. Find out why more than 200 million users trust TeamViewer! Free for... Read more
Viber 4.1.0 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device,... Read more
Apple iOS 7.1.1 - The latest version of...
The latest version of iOS can be downloaded through iTunes. Apple iOS 7 brings an all-new design and all-new features. Simplicity Simplicity is often equated with minimalism. Yet true simplicity is... Read more
1Password 4.3 - Powerful password manage...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Lens Blur 1.3.0 - True out-of-focus boke...
Let Lens Blur transform your existing photo into true SLR-quality out-of-focus bokeh effect! Everyone needs a gorgeous personalized background for a social profile, blog, Web/UI design, presentation... Read more
VMware Fusion 6.0.3 - Run Windows apps a...
VMware Fusion allows you to create a Virtual Machine on your Mac and run Windows (including Windows 8.1) and Windows software on your Mac. Run your favorite Windows applications alongside Mac... Read more

Latest Forum Discussions

See All

Yomi Review
Yomi Review By Rob Thomas on April 24th, 2014 Our Rating: :: C-C-C-COMBO BREAKERiPad Only App - Designed for the iPad Round One – Fight! No quarters required for this iOS adaptation of a tabletop adaptation of the arcade fighting... | Read more »
Injustice: Gods Among Us Updated with Ne...
Injustice: Gods Among Us Updated with New Characters, Leaderboards, Gear, and Online Multiplayer Posted by Rob Rich on April 24th, 2014 [ | Read more »
Spin It Review
Spin It Review By Jordan Minor on April 24th, 2014 Our Rating: :: SPIN ME RIGHT ROUNDUniversal App - Designed for iPhone and iPad Spin It has a fine puzzle game model, but its execution lacks energy.   | Read more »
Productivity App NoteSuite is Having its...
Productivity App NoteSuite is Having its Biggest Sale Ever, Just for One Week Posted by Rob Rich on April 24th, 2014 [ permalink ] | Read more »
Wayward Souls Review
Wayward Souls Review By Carter Dotson on April 24th, 2014 Our Rating: :: CARRY ON, WAYWARD SONUniversal App - Designed for iPhone and iPad Wayward Souls is a roguelike-inspired action-RPG that sets a high bar for other games to... | Read more »
The Sandbox Gets Update, Receives New Ca...
The Sandbox Gets Update, Receives New Campaign and New Elements Posted by Tre Lawrence on April 24th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Football Management Simulator One For El...
Football Management Simulator One For Eleven Released Worldwide Today for iOS Posted by Simon Reed on April 24th, 2014 [ permalink ] Free-To-Play football management title One For E | Read more »
Leo’s Fortune Review
Leo’s Fortune Review By Jordan Minor on April 24th, 2014 Our Rating: :: FORTUNATE SONUniversal App - Designed for iPhone and iPad Leo’s Fortune delivers a platforming experience as creative and refined as any console game.   | Read more »
Suited Up (Games)
Suited Up 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Suited Up is a difficult, one-touch platformer that requires players to visualize each jump. The controls in Suited Up are simple,... | Read more »
MyTP One Mountain - Ski, Freeski and Sno...
MyTP One Mountain - Ski, Freeski and Snowboard 1.0.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0.0 (iTunes) Description: As real snow is melting away in the snow parks around the northern hemisphere, it's now time... | Read more »

Price Scanner via MacPrices.net

16GB 1st generation iPad mini available for $...
Radio Shack has a select number of refurbished 1st generation 16GB WiFi iPad minis available for $199.99 on their online store. Choose free shipping or free ship-to-store. We expect these to sell out... Read more
13-inch 2.5GHz MacBook Pro on sale for $100 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $1099 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
iPad Sales “Lull” A Reality Correction Of Unm...
I have lots of time for Jean-Louis Gassée, the former Apple Computer executive (1981 to 1990) who succeeded Steve Jobs as head of Macintosh development when the latter was dismissed in 1985. Mr.... Read more
Apple Makes OS X Betas Available To All – Wit...
Apple’s OS X Beta Seed Program, which lets you install the latest pre-release builds, try it out, and submit your feedback, is now open to anyone who wants to sign on rather than to developers and... Read more
Apple Releases iOS 7.1.1 Update
The latest iOS 7.1.1 update contains improvements, bug fixes and security updates, including: • Further improvements to Touch ID fingerprint recognition • Fixes a bug that could impact keyboard... Read more
Logitech Announces Thinner, Lighter, More Fle...
Logitech has announced an update to its Ultrathin for iPad Air, iPad mini and iPad mini with Retina display, improving the flexibility and design of its award-winning predecessor with an even thinner... Read more
Logitech Introduces Hinge, Big Bang and Turna...
Logitech has announced expansion of its tablet product line with three new cases – the Logitech Hinge, the Logitech Big Bang and the Logitech Turnaround – each for the iPad Air, iPad mini and iPad... Read more
WaterField’s Rough Rider Leather Messenger Ba...
WaterField Designs have announced the new 15-inch size of their popular Rough Rider leather messenger bag, a vintage-looking bag that combines Old West charm and ruggedness with distinctly modern... Read more
New Mac Pro on sale, save $100 on the 4-Core...
J&R has the new 4-Core Mac Pro in stock today and on sale for $2899 including free shipping plus NY sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this... Read more
Apple refurbished iMacs available for up to $...
The Apple Store has Apple Certified Refurbished 2013 iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. - 27″ 3.4GHz iMac – $1699... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**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 (ASC) - Apple (...
**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
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**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* Inc. Research Data Specialist - Appl...
…of Worldwide Market Research & Intelligence. The team is responsible for conducting Apple branded consumer market research. It is also responsible for analyzing data Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.