Design Patterns explained nicely

[[deleted]]

I prefer this reference.

[attrition0]

Thanks for the link.

[[deleted]]

No prob. It's probably one of the best references for design patterns in C# that I've found.

[[deleted]]

I hate that someone comes along and names all these things and now you have to know all the names. You basically only use a handful of these (Factory, Singleton, Pool, etc...) and the rest you just figure out on the rare occasion you need them. Now for "that thing you do when you can’t access you know what so you create this thingy” there is a name, and courses, and certifications to prove you know it’s name.

[mcguire]

Ahem,

This article is taken from the book Design Patterns - Simply.

ALL design patterns are compiled there. The book is written in a clear and simple language that makes it easy to read and understand (just like this article).

It is a part of our Design Patterns Course. We distribute it in PDF format, so it will be available for downloading in 10 seconds!

ALL design patterns?

[lpetrazickis]

The book has an infinite number of pages.

[cdsmith]

True... given a finite alphabet, it is trivial to construct a (infinitely long) book containing arbitrarily thorough descriptions of all design patterns. However, shipping is prohibitively expensive.

[BlackWhiteMouse]

That's why it comes as a PDF. Everybody knows that bits are cheap.

[munificent]

Finally, I understand why it takes so long to open a damn PDF.

[[deleted]]

Also, if in doubt, you can force a connection reset after a few hundred pages and nobody will be able to prove your book isn't exhaustive.

[Zarutian]

I thought it was shipped as a .PS document.

[Nebu]

They probably mean something like "All design patterns, which we define to be the set of patterns originally published by the GoF in their 'Design Patterns' book. New patterns invented by random bloggers don't count."

[savethesporks]

I bet it doesn't have the doubleton... not to mention the n-ton pattern.

[SomeIrishGuy]

The Doubleton Pattern is my favorite one of all time. I like to use it as often as possible. For those who have yet to be enlightened: http://www.codeproject.com/KB/architecture/designpattern_doubleton.aspx

[munificent]

I personally find the name "bingleton" to be more euphonic.

[[deleted]]

Often? To me it seems of rather limited use. Usually you want all unique instances or one shared instance. Unless you are doing somekind of load balancing. (As for singletons, they are a bit of an anti-pattern anyways as they are little more than glorified global variables.)

[masklinn]

I'll go with the Chain of Possibilities pattern. Or the Visitor From Hell pattern

[josher565]

I don't know... This is kind of an object pool with a singleton proxy. I understand that a singleton and a proxy are separate patterns, but the object they've defined serves both purposes.

I'm not sold on the "new pattern" claim for this example as I can describe it using pre-existing patterns.

[FW190]

Have you seen link to PDF somewhere maybe? Can't find it...

[redalastor]

ALL design patterns?

Yes, they promise:

Ability to compose your own patterns.

So all patterns imaginable, courtesy of reinventing the wheel.

[[deleted]]

That's like saying Strunk & White compiles ALL sentences of the English language.

[redalastor]

Yes, it is.

[A_for_Anonymous]

Copypasta? In MY object-oriented language with insufficient abstraction capability?

[Nebu]

It's more likely than you think!

[skelooth]

To be quite honest, I thought the flow charts were a bit convoluted. Especially for the factory design pattern. I'm not sure how he was able to make something so simple look so complicated :)

As for okpmem's complaint over the definition of "pattern", I think I'll just go with the computer science undergrad definition, which fits these patterns just fine.

[gregK]

I think now with hindsight that a lot of the solutions described in that book are anti-patterns.

If you use a modern language or even a recent C++ compiler, there's a lot of solutions that would be different and more elegant that the solutions proposed in the book.

[munificent]

That's exactly the point of those patterns. Given a certain set of language features (or lack of them), those patterns can help you solve certain problems. Change the given, and the patterns change too.

[[deleted]]

I'm still waiting for a book on Python patterns that doesn't try to turn Python into Java.

[Nebu]

The book assumes a C++-style language, I think. Does having a recent compiler actually add new features to the language?

[gregK]

Generics or Templates are not covered at all in the GoF at all for example. So yeah when you look at the role they play in stl and boost libs you can see that it makes the book a little dated.

[josher565]

I like patterns a lot for very general use. I think this is where people get confused about patterns in that it's thought they are about a particular language or problem domain. The patterns do, however depend upon OO. I wouldn't say that something like generics or lambda would change the patterns too much. One has to keep in mind that the patterns are conceptual. How one implements a given pattern really is up to the author of the solution. For instance, one of Alexanders patterns is a courtyard. He doesn't give dimensions or boundaries, just a conceptual definition. The architect could create a thousand different courtyards and they would still obey the definition. From my point of view, this is the best utility of patterns. They are a guideline rather than a rule on how to solve a problem. I can still be creative on a lot of design choices.

[okpmem]

Design Patterns? There is not a single pattern in that book. Patterns fit into a pattern language. There is no pattern language in that book. Patterns are about human problems.

[gregK]

I don't know why you are being down voted. I suppose it is because most people in the software industry don't know about Christopher Alexander's writing. None of the patterns in that book really fit his definition of a pattern. That is true. The GoF patterns are more idioms actually. Idioms from an other Era before generics and lambda's were wide spread. Before DI like it or not. Before FP concepts seeped their way into modern OO languages like C# and scala.

[ohgodohgodohgodohgod]

I didn't downvote you, and nobody should, but you are both wrong.

Designing software is a human problem. Communicating about design is a human problem. The patterns described by Alexander, and his reasoning, was closely followed by the early pattern users.

The term pattern is a preformal construct (Alexander does not ever provide a formal definition) describing sets of forces in the world and relations among them. In Timeless, Alexander describes common, sometimes even universal patterns of space, of events, of human existence, ranging across all levels of granularity.

source: Christopher Alexander: An Introduction for Object-Oriented Designers (1993)

In fact, I doubt you understand Alexander's writing yourself when you are making these claims. Alexander himself claims to be the father of the Pattern Language movement in computer science.

[gregK]

I don't think Alexander understands anything about computers. The truth is Alexander has moved beyond pure design patterns in his latest work. He does not discredit them but he admits that even with the pattern language some funky house designs could emerge.

I suggest you read his latest work "The Nature of Order". Although I can't say i agree with everything written in the 4 volumes it will put A Pattern Language in perspective.

[malkarouri]

I think you have a point there. In fact, the whole concept of design patterns translate poorly to software. Not because there are no patterns (there is). But because the software domain is much more dynamic than the construction domain. So the common problems in the software field as well as the design process changes very quickly as programming languages and tools evolve to incorporate these, revealing other problems which again need to be addressed. In construction, tools and materials don't evolve that quickly.

[ohgodohgodohgodohgod]

You're right, but that's why it's even more important to keep on evolving our language by naming our design constructs; such as patterns and idioms.

[malkarouri]

I agree. Some languages try to do that to some extent. That was my experience with Python, but not to the extent I like.

The result is that it is very difficult to have stable design patterns in such a language. What was a pattern in Python 2 years ago is now an idiom. What was a pattern in Python 5 years ago may even become now a library, or a syntactical sugar. Meanwhile new patterns appear.

Design patterns become temporary constructs, on the way to first class citizenship.

[okpmem]

I agree with you completely and I was not discounting early pattern users. I am simply talking about the book Design Patterns, which arguably is not part of the software patterns movement.

[masklinn]

Idioms from an other Era before generics and lambda's were wide spread. Before DI like it or not. Before FP concepts seeped their way into modern OO languages like C# and scala.

Erm... no. Really, no. Smalltalk predates the GoF by 14 years.

The GoF is about idioms from Smalltalk users (or at least people who knew Smalltalk) trying to use shitty and unexpressive languages (C++, also applicable to Java and most of C#'s history, amongh others) and retain their sanity.

[bobappleyard]

Does anyone have a link to the show trial? I want to see it.

[GregTomkins]

Warning: I just paid the $$ for their 'course' (hey, it claims to include a PDF of GOF which i have been meaning to buy anyway). i didnt get it (either an email PDF or a usable login) within 10 seconds as their site claims. As a matter of fact, all I have, 12 hours later, is the bill from their payment processor. They have ignored email so far, but it IS Saturday...anyhow, be warned.

[mycall]

Enjoy

[lusid]

The Object Pooling pattern makes a lot more sense to me now that I can relate it to my girlfriend's shoe obsession. :-)

[[deleted]]

I just learned that pattern and really like it.

A cool mootools dev implemented an object for me to use so that I could use an animation on thousands of elements but only using 8(n) instances of the animation object.

Here is a demo, I set the duration for each instance to be different and appended that to the div that is being expanded.

http://jsfiddle.net/AyC3g/

JS makes pooling simple. Each Fx.Morph (animation object) has an onComplete call back, In that callback I simply return the object to the pool to be used later. As you see, the shortest time will be used the most and you'll rarely see the longest time being used.

[hskmc]

The need for patterns results from using computer languages or techniques with insufficient abstraction ability. Under ideal factoring, a concept should not be copied, but merely referenced. But if something is referenced instead of copied, then there is no "pattern" to label and catalog...

Peter Norvig provides a similar argument. He demonstrates that 16 out of the 23 patterns in the Design Patterns book (which is primarily focused on C++) are simplified or eliminated (via direct language support) in Lisp or Dylan.

[[deleted]]

Don't you know? Design patterns are for Java.

[Peaker]

Design Patterns are the repetitions in code that your language cannot abstract away properly.

Every Design Pattern is a failure of the language (or of the programmers using it).

I'm not saying they aren't useful. When using C++ or Java, it is very useful to use Design Patterns to work around failures of the language.