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• Looking for a small, light scene graph style abstraction lib for shader based OpenGL

  - by Pris

  I'm looking for a 'lean and mean' c/c++ scene graph library for OpenGL that doesn't use any deprecated functionality. It should be cross platform (strictly speaking I just dev on Linux so no love lost if it doesn't work on Windows), and it should be possible to deploy to mobile targets (ie OpenGLES2, and no crazy mandatory dependencies that wouldn't port well to modern mobile frameworks like iOS, Android, etc), with a license that's compatible with closed source software (LGPL or more liberal). Specific nice-to-haves would be: Cameras and Viewers (trackball, fly-by, etc) Object transform hierarchies (if B is a child of A, and you move A, B has the same transform applied to it) Simple animation Scene optimization (frustum culling, use VBOs, minimize state changes, etc) Text I've played around with OpenSceneGraph a lot and it's pretty amazing for fixed function pipeline stuff, but I've had a few of problems using it with the programmable pipeline and after going through their mailing list, it seems several people have had similar issues (going back years). Kitware's VES looks neat (http://www.vtk.org/Wiki/VES), but VES + VTK is pretty heavy. VTK is also typically for analyzing scientific data and I've read that it's not that appropriate for a general use case (not that great at rendering a lot of objects on scene,etc) I'm currently looking at VisualizationLibrary (http://www.visualizationlibrary.org/documentation/pag_gallery.html) which looks like it offers some of the functionality I'd like, but it doesn't explicitly support mobile targets. Other solutions like Ogre, Horde3D, Irrlicht, etc tend to be full on game engines and that's not really what I'm looking for. I'd like some suggestions for other libraries that I may have missed... please note I'm not willing to roll my own solution from scratch.

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• Why is cleverness considered harmful in programming by some people?

  - by Larry Coleman

  I've noticed a lot of questions lately relating to different abstraction techniques, and answers saying basically that the techniques in question are "too clever." I would think that part of our jobs as programmers is to determine the best solutions to the problems we are given to solve, and cleverness is helpful in doing that. So my question is: are the people who think certain abstraction techniques are too clever opposed to cleverness per se, or is there some other reason for the objection? EDIT: This parser combinator is an example of what I would consider to be clever code. I downloaded this and looked it over for about half an hour. Then I stepped through the macro expansion on paper and saw the light. Now that I understand it, it seems much more elegant than the Haskell parser combinator.

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• How Does One Make Scala Control Abstraction in Repeat Until?

  - by peter_pilgrim

  Hi I am Peter Pilgrim. I watched Martin Odersky create a control abstraction in Scala. However I can not yet seem to repeat it inside IntelliJ IDEA 9. Is it the IDE? package demo class Control { def repeatLoop ( body: = Unit ) = new Until( body ) class Until( body: = Unit ) { def until( cond: = Boolean ) { body; val value: Boolean = cond; println("value="+value) if ( value ) repeatLoop(body).until(cond) // if (cond) until(cond) } } def doTest2(): Unit = { var y: Int = 1 println("testing ... repeatUntil() control structure") repeatLoop { println("found y="+y) y = y + 1 } { until ( y < 10 ) } } } The error message reads: Information:Compilation completed with 1 error and 0 warnings Information:1 error Information:0 warnings C:\Users\Peter\IdeaProjects\HelloWord\src\demo\Control.scala Error:Error:line (57)error: Control.this.repeatLoop({ scala.this.Predef.println("found y=".+(y)); y = y.+(1) }) of type Control.this.Until does not take parameters repeatLoop { In the curried function the body can be thought to return an expression (the value of y+1) however the declaration body parameter of repeatUntil clearly says this can be ignored or not? What does the error mean?

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• Thick models Vs. Business Logic, Where do you draw the distinction?

  - by TokenMacGuy

  Today I got into a heated debate with another developer at my organization about where and how to add methods to database mapped classes. We use sqlalchemy, and a major part of the existing code base in our database models is little more than a bag of mapped properties with a class name, a nearly mechanical translation from database tables to python objects. In the argument, my position was that that the primary value of using an ORM was that you can attach low level behaviors and algorithms to the mapped classes. Models are classes first, and secondarily persistent (they could be persistent using xml in a filesystem, you don't need to care). His view was that any behavior at all is "business logic", and necessarily belongs anywhere but in the persistent model, which are to be used for database persistence only. I certainly do think that there is a distinction between what is business logic, and should be separated, since it has some isolation from the lower level of how that gets implemented, and domain logic, which I believe is the abstraction provided by the model classes argued about in the previous paragraph, but I'm having a hard time putting my finger on what that is. I have a better sense of what might be the API (which, in our case, is HTTP "ReSTful"), in that users invoke the API with what they want to do, distinct from what they are allowed to do, and how it gets done. tl;dr: What kinds of things can or should go in a method in a mapped class when using an ORM, and what should be left out, to live in another layer of abstraction?

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• Too complex/too many objects?

  - by Mike Fairhurst

  I know that this will be a difficult question to answer without context, but hopefully there are at least some good guidelines to share on this. The questions are at the bottom if you want to skip the details. Most are about OOP in general. Begin context. I am a jr dev on a PHP application, and in general the devs I work with consider themselves to use many more OO concepts than most PHP devs. Still, in my research on clean code I have read about so many ways of using OO features to make code flexible, powerful, expressive, testable, etc. that is just plain not in use here. The current strongly OO API that I've proposed is being called too complex, even though it is trivial to implement. The problem I'm solving is that our permission checks are done via a message object (my API, they wanted to use arrays of constants) and the message object does not hold the validation object accountable for checking all provided data. Metaphorically, if your perm containing 'allowable' and 'rare but disallowed' is sent into a validator, the validator may not know to look for 'rare but disallowed', but approve 'allowable', which will actually approve the whole perm check. We have like 11 validators, too many to easily track at such minute detail. So I proposed an AtomicPermission class. To fix the previous example, the perm would instead contain two atomic permissions, one wrapping 'allowable' and the other wrapping 'rare but disallowed'. Where previously the validator would say 'the check is OK because it contains allowable,' now it would instead say '"allowable" is ok', at which point the check ends...and the check fails, because 'rare but disallowed' was not specifically okay-ed. The implementation is just 4 trivial objects, and rewriting a 10 line function into a 15 line function. abstract class PermissionAtom { public function allow(); // maybe deny() as well public function wasAllowed(); } class PermissionField extends PermissionAtom { public function getName(); public function getValue(); } class PermissionIdentifier extends PermissionAtom { public function getIdentifier(); } class PermissionAction extends PermissionAtom { public function getType(); } They say that this is 'not going to get us anything important' and it is 'too complex' and 'will be difficult for new developers to pick up.' I respectfully disagree, and there I end my context to begin the broader questions. So the question is about my OOP, are there any guidelines I should know: is this too complicated/too much OOP? Not that I expect to get more than 'it depends, I'd have to see if...' when is OO abstraction too much? when is OO abstraction too little? how can I determine when I am overthinking a problem vs fixing one? how can I determine when I am adding bad code to a bad project? how can I pitch these APIs? I feel the other devs would just rather say 'its too complicated' than ask 'can you explain it?' whenever I suggest a new class.

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• Using High Level Abstractions

  - by Jonn

  I'm not sure if I'm using the correct term, but would you program using High-level abstractions like Powerbuilder, or some CMS like MODx or DotNetNuke? I haven't dabbled in any of these yet. The reason I'm asking is that I kind of feel intimidated by the whole notion of using any abstraction over the languages I'm using. I'm thinking that my job might be over-simplified. While it may provide business solutions faster, I'd rather be coding straight from, in my case, .NET. Do/Would you use abstractions like these or prefer them over programming in lower level languages?

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• Is there a standard for machine-readable descriptions of RESTful services?

  - by ecmendenhall

  I've interacted with a few RESTful APIs that provided excellent documentation for humans and descriptive URIs, but none of them seem to return machine-readable descriptions of themselves. It's not too tough to write methods of my own that assemble the right paths, and many language-specific API libraries are already just wrappers around RESTful requests. But the next level of abstraction seems really useful: a library that could read in an API's own machine readable documentation and generate the wrappers automatically, perhaps with a call to some standard URI like base_url + '/documentation' Are there any standards for machine-readable API documentation? Am I doing REST wrong? I am a relatively new programmer, but this seems like a good idea.

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• Should I use an interface when methods are only similar?

  - by Joshua Harris

  I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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• What is Caliburn Validation abstraction

  - by Chen Kinnrot

  Recently I saw this document that specify how great is Caliburn(Not really it compares it to the micro framework, and thats enough). I'm working with Caliburn for more than a year and don't know many things about it. So maybe someone can explain the following(Some of it I can understand but have no iea about the relation to caliburn): Validation abstraction module framework ExpressionTree-Based runtime delegate generation ViewModelFactory ShellFramework I'm working with V1.1 so if something is new in 2.0, just say it belong to the new version I'll learn it probably in the future.

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• is there an abstraction layer for XML?

  - by ajsie

  i wonder if there is a good abstraction layer for XLM like ORM for databases? is it a good solution or is it better to use simple_xml for xml CRUD?

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• abstraction and encapsulation in asp.net?

  - by Surya sasidhar

  hi, when we write all our application methods and variables in a classes is nothing but data abstraction and encapsulation. Is it right?

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• What's the real benefit of meta-modeling?

  - by Jakob

  After reading several texts about meta-modeling I still do not really get the practical benefit. Sometimes I think it is only an interesting mind game but no useful tool. Sure it is wise to clarify your modeling vocabulary: some may say class where others say entity or concept, but this is just simple documentation your modeling terminology. Meta-modeling, as I understand it, is more complex, as it tries to formalize and abstract modeling. Some good examples are Keet's formal comparison of conceptual data modeling languages (UML, ERM and ORM) from academia and the Meta Object Facility (MOF) from industry. To me MOF looks as impractical as CORBA, which was also created by OMG. In theory you could use meta-modeling to transform and integrate models in different modeling languages, but is anyone actually doing this?

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• Abstract Data Type and Data Structure

  - by mark075

  It's quite difficult for me to understand these terms. I searched on google and read a little on Wikipedia but I'm still not sure. I've determined so far that: Abstract Data Type is a definition of new type, describes its properties and operations. Data Structure is an implementation of ADT. Many ADT can be implemented as the same Data Structure. If I think right, array as ADT means a collection of elements and as Data Structure, how it's stored in a memory. Stack is ADT with push, pop operations, but can we say about stack data structure if I mean I used stack implemented as an array in my algorithm? And why heap isn't ADT? It can be implemented as tree or an array.

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• Is there a more intelligent way to do this besides a long chain of if statements or switch?

  - by Harrison Nguyen

  I'm implementing an IRC bot that receives a message and I'm checking that message to determine which functions to call. Is there a more clever way of doing this? It seems like it'd quickly get out of hand after I got up to like 20 commands. Perhaps there's a better way to abstract this? public void onMessage(String channel, String sender, String login, String hostname, String message){ if (message.equalsIgnoreCase(".np")){ // TODO: Use Last.fm API to find the now playing } else if (message.toLowerCase().startsWith(".register")) { cmd.registerLastNick(channel, sender, message); } else if (message.toLowerCase().startsWith("give us a countdown")) { cmd.countdown(channel, message); } else if (message.toLowerCase().startsWith("remember am routine")) { cmd.updateAmRoutine(channel, message, sender); } }

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• Why doesn't Haskell have type-level lambda abstractions?

  - by Petr Pudlák

  Are there some theoretical reasons for that (like that the type checking or type inference would become undecidable), or practical reasons (too difficult to implement properly)? Currently, we can wrap things into newtype like newtype Pair a = Pair (a, a) and then have Pair :: * -> * but we cannot do something like ?(a:*). (a,a). (There are some languages that have them, for example, Scala does.)

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• Is there a canonical book on general abstractions and modeling?

  - by David The Man

  I've been trying to understand the fundamentals of general abstractions and modeling: there are quite a lot of books when you search for abstractions, but most of those seem to be about learning object-oriented programming in a given language. Is there a book out there that's the de-facto standard for describing best practices, design methodologies, and other helpful information about general abstractions and modeling? What about that book makes it special?

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• Is dependency injection by hand a better alternative to composition and polymorphism?

  - by Drake Clarris

  First, I'm an entry level programmer; In fact, I'm finishing an A.S. degree with a final capstone project over the summer. In my new job, when there isn't some project for me to do (they're waiting to fill the team with more new hires), I've been given books to read and learn from while I wait - some textbooks, others not so much (like Code Complete). After going through these books, I've turned to the internet to learn as much as possible, and started learning about SOLID and DI (we talked some about Liskov's substitution principle, but not much else SOLID ideas). So as I've learned, I sat down to do to learn better, and began writing some code to utilize DI by hand (there are no DI frameworks on the development computers). Thing is, as I do it, I notice it feels familiar... and it seems like it is very much like work I've done in the past using composition of abstract classes using polymorphism. Am I missing a bigger picture here? Is there something about DI (at least by hand) that goes beyond that? I understand the possibility of having configurations not in code of some DI frameworks having some great benefits as far as changing things without having to recompile, but when doing it by hand, I'm not sure if it's any different than stated above... Some insight into this would be very helpful!

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• Abstract Factory Method and Polymorphism

  - by Scotty C.

  Being a PHP programmer for the last couple of years, I'm just starting to get into advanced programming styles and using polymorphic patterns. I was watching a video on polymorphism the other day, and the guy giving the lecture said that if at all possible, you should get rid of if statements in your code, and that a switch is almost always a sign that polymorphism is needed. At this point I was quite inspired and immediately went off to try out these new concepts, so I decided to make a small caching module using a factory method. Of course the very first thing I have to do is create a switch to decide what file encoding to choose. DANG! class Main { public static function methodA($parameter='') { switch ($parameter) { case 'a': $object = new \name\space\object1(); break; case 'b': $object = new \name\space\object2(); break; case 'c': $object = new \name\space\object3(); break; default: $object = new \name\space\object1(); } return (sekretInterface $object); } } At this point I'm not really sure what to do. As far as I can tell, I either have to use a different pattern and have separate methods for each object instance, or accept that a switch is necessary to "switch" between them. What do you guys think?

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• Should concrete classes avoid calling other concrete classes, except for data objects?

  - by Kazark

  In Appendix A to The Art of Unit Testing, Roy Osherove, speaking about ways to write testable code from the start, says, An abstract class shouldn't call concrete classes, and concerete classes shouldn't call concrete classes either, unless they're data objects (objects holding data, with no behavior). (259) The first half of the sentence is simply Dependency Inversion from SOLID. The second half seems rather extreme to me. That means that every time I'm going to write a class that isn't a simple data structure, which is most classes, I should write an interface or abstract class first, right? Is it really worthwhile to go that far in defining abstract classes an interfaces? Can anyone explain why in more detail, or refute it in spite of its benefit for testability?

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• Understanding the levels of computing

  - by RParadox

  Sorry, for my confused question. I'm looking for some pointers. Up to now I have been working mostly with Java and Python on the application layer and I have only a vague understanding of operating systems and hardware. I want to understand much more about the lower levels of computing, but it gets really overwhelming somehow. At university I took a class about microprogramming, i.e. how processors get hard-wired to implement the ASM codes. Up to now I always thought I wouldn't get more done if learned more about the "low level". One question I have is: how is it even possible that hardware gets hidden almost completely from the developer? Is it accurate to say that the operating system is a software layer for the hardware? One small example: in programming I have never come across the need to understand what L2 or L3 Cache is. For the typical business application environment one almost never needs to understand assembler and the lower levels of computing, because nowadays there is a technology stack for almost anything. I guess the whole point of these lower levels is to provide an interface to higher levels. On the other hand I wonder how much influence the lower levels can have, for example this whole graphics computing thing. So, on the other hand, there is this theoretical computer science branch, which works on abstract computing models. However, I also rarely encountered situations, where I found it helpful thinking in the categories of complexity models, proof verification, etc. I sort of know, that there is a complexity class called NP, and that they are kind of impossible to solve for a big number of N. What I'm missing is a reference for a framework to think about these things. It seems to me, that there all kinds of different camps, who rarely interact. The last few weeks I have been reading about security issues. Here somehow, much of the different layers come together. Attacks and exploits almost always occur on the lower level, so in this case it is necessary to learn about the details of the OSI layers, the inner workings of an OS, etc.

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• Designing communications for extensibility

  - by Thomas S.

  I am working on the design stages of an application that will a) collect data from various sources (in my case that's scientific data from serial ports), keeping track of the age of the data, b) generate real-time statistics (e.g. running averages) c) display, record, and otherwise handle the data (and statistics). I anticipate that I will be adding both data producers and consumers over time, and would like to design this application abstractly so that I will be able to trivially add functionality with a small amount of interface code. What I'm stumbling on is deciding what communication infrastructure I should use to handle the interfaces. In particular, how should I make the processed data and statistics available to multiple consumers? Some things I've considered: Writing to several named pipes (variable number). Each consumer reads from one of them. Using FUSE to make a userspace filesystem where a read() returns the latest line of data even if another process has already read it. Making a TCP server, and having consumers connect and request data individually. Simply writing the consumers as part of the same program that aggregates the data. So I would like to hear your all's advice on deciding how to interface these functions in the best way to keep them separate and allow room for extenstions.

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• Why does this article state that graduate education liberate one from concerns like the efficiency of hardware-based integers?

  - by kadaj

  Quoting The Evolution of Haskell Programmer, graduate education tends to liberate one from petty concerns about, e.g., the efficiency of hardware-based integers What exactly does this suggest? Is it that after graduation, one gets more interested in abstract ideas so much that he does not think hardware is relevant? Or that hardware is also abstracted and one is more interested in algorithms? I am trying to understand on what grounds the sentence is based.

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• I have data that sends in "bursts" of 100 records with a significant delay. How do I structure my classes for multithreading?

  - by makerofthings7

  My datasource sends information in 100 batches of 100 records with a delay of 1 to 3 seconds between batches. I would like to start processing data as soon as it's received, but I'm not sure how to best approach this. Some ideas I've been playing with include: yield Concurrent Dictionary ConcurrentDictionary with INotifyProperyChanged Events etc. As you can see I'm all over the place, and would appreciate some tested guidance on how to approach this

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• Case class copy() method abstraction.

  - by Joa Ebert

  I would like to know if it is possible to abstract the copy method of case classes. Basically I have something like sealed trait Op and then something like case class Push(value: Int) extends Op and case class Pop() extends Op. The first problem: A case class without arguments/members does not define a copy method. You can try this in the REPL. scala> case class Foo() defined class Foo scala> Foo().copy() <console>:8: error: value copy is not a member of Foo Foo().copy() ^ scala> case class Foo(x: Int) defined class Foo scala> Foo(0).copy() res1: Foo = Foo(0) Is there a reason why the compiler makes this exception? I think it is rather unituitive and I would expect every case class to define a copy method. The second problem: I have a method def ops: List[Op] and I would like to copy all ops like ops map { _.copy() }. How would I define the copy method in the Op trait? I get a "too many arguments" error if I say def copy(): this.type. However, since all copy() methods have only optional arguments: why is this incorrect? And, how do I do that correct? By making another method named def clone(): this.type and write everywhere def clone() = copy() for all the case classes? I hope not.

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• MSMQ - Message Queue Abstraction and Pattern

  - by Maxim Gershkovich

  Hi All, Let me define the problem first and why a messagequeue has been chosen. I have a datalayer that will be transactional and EXTREMELY insert heavy and rather then attempt to deal with these issues when they occur I am hoping to implement my application from the ground up with this in mind. I have decided to tackle this problem by using the Microsoft Message Queue and perform inserts as time permits asynchronously. However I quickly ran into a problem. Certain inserts that I perform may need to be recalled (ie: retrieved) immediately (imagine this is for POS system and what happens if you need to recall the last transaction - one that still hasn’t been inserted). The way I decided to tackle this problem is by abstracting the MessageQueue and combining it in my data access layer thereby creating the illusion of a single set of data being returned to the user of the datalayer (I have considered the other issues that occur in such a scenario (ie: essentially dirty reads and such) and have concluded for my purposes I can control these issues). However this is where things get a little nasty... I’ve worked out how to get the messages back and such (trivial enough problem) but where I am stuck is; how do I create a generic (or at least somewhat generic) way of querying my message queue? One where I can minimize the duplication between the SQL queries and MessageQueue queries. I have considered using LINQ (but have very limited understanding of the technology) and have also attempted an implementation with Predicates which so far is pretty smelly. Are there any patterns for such a problem that I can utilize? Am I going about this the wrong way? Does anyone have an of their own ideas about how I can tackle this problem? Does anyone even understand what I am talking about? :-) Any and ALL input would be highly appreciated and seriously considered… Thanks again.

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