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• Didatic approaches to teach versioning with Git

  - by Herberth Amaral

  I have already taught versioning with Git, but I think it could be more enjoyable for the guys I teach if I use another approach to teach them. The guys I mentioned before were used to working with SVN and I tried to teach Git based on SVN. Not such a good idea. It seems that some guys/teams which use SVN need a re-education on version control when they're learning Git or another DCVCS. In another attempt, I tried to show a scenario where a development team try to work without a (D)VCS and then I showed how their lives could be easier if they used a (D)VCS. I had the impression that part of the audience left the presentation without a clue what I was talking about. I've taught other classes on other subjects without problems, so I think this is not a issue with me as a teacher, but with my method. I know Git and versioning as well I know the other subjects I've presented to the other classes. So, basically, how to teach Git/DCVCS? Start with some diffs/patches and manual versioning and then teach how it can be more productive with Git? Start with Git object model? Or try to start with some pretty commands and try to save some time? To be clear: I'm looking for approaches on how to teach DCVCS (focusing on Git) effectively, based on real experiences.

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• Node.JS testing with Jasmine, databases, and pre-existing code

  - by Jim Rubenstein

  I've recently built the start of a core system which is likely going turn into a monster product. I'm building the system with node.js, and decided after I got a small base built, that It'd be a great idea to start using some sort of automated test suite to test the application. I decided to use jasmine, as it seems pretty solid and has a lot of features for stubbing spying and mocking methods and classes. The application has a lot of external data stores and api access (kestrel, mysql, mongodb, facebook, and more). My issue is, I've got a good amount of code written that I want to start testing - as it represents the underpinnings of the application. What are the best practices for testing methods/classes that access external APIs that I may or may not have control over? As an example, I have a data structure that fetches a bunch of data from a MySQL database. I want to test the method that retrieves the data; and I'm not sure how to go about it. I could test the fetch method which is supposed to return an array of objects, but to isolate the method from the database, I need to define my own fixture data. So what I end up doing is stubbing the mysql execution, and returning a static dataset. So, I end up writing a function that returns the dataset that makes my test pass. That doesn't seem to actually test the code, other than verifying a method is being called. I know this is kind of abstract and vague, it seems that the idea of testing is very much abstract though, so hopefully someone has some experience and can guide me in the right direction. Any advice, or reading I can do is more than welcomed. Thanks in advance.

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• HTML5 data-* (custom data attribute)

  - by Renso

  Goal: Store custom data with the data attribute on any DOM element and retrieve it. Previously under HTML4 we used to use classes to store custom data, something to the affect of <input class="account void limit-5000 over-4999" /> and then have to parse the data out of the class In a book published by Peter-Paul Koch in 2007, ppk on JavaScript, he explains why and how to use custom attributes to make data more accessible to JavaScript, using name-value pairs. Accessing a custom attribute account-limit=5000 is much easier and more intuitive than trying to parse it out of a class, Plus, what if the class name for example "color-5" has a representative class definition in a CSS stylesheet that hides it away or worse some JavaScript plugin that automatically adds 5000 to it, or something crazy like that, just because it is a valid class name. As you can see there are quite a few reasons why using classes is a bad design and why it was important to define custom data attributes in HTML5. Syntax: You define the data attribute by simply prefixing any data item you want to store with any HTML element with "data-". For example to store our customers account data with a hidden input element: <input type="hidden" data-account="void" data-limit=5000 data-over=4999  /> How to access the data: account  -     element.dataset.account limit    -     element.dataset.limit You can also access it by using the more traditional get/setAttribute method or if using jQuery $('#element').attr('data-account','void') Browser support: All except for IE. There is an IE hack around this at http://gist.github.com/362081. Special Note: Be AWARE, do not use upper-case when defining your data elements as it is all converted to lower-case when reading it, so: data-myAccount="A1234" will not be found when you read it with: element.dataset.myAccount Use only lowercase when reading so this will work: element.dataset.myaccount

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• Object oriented EDI handling in PHP

  - by Robert van der Linde

  I'm currently starting a new sub project where I will: Retrieve the order information from our mainframe Save the order information to our web-apps' database Send the order as EDI (either D01b or D93a) Receive the order response, despatch advice and invoice messages Do all kinds of fun things with the resulting datasets. However I am struggling with my initial class designs. The order information will be retrieved from the mainframe which will result in a "AOrder" class, this isn't a problem, I am not sure about how to mold this local object into an EDI string. Should I create EDIOrder/EDIOrderResponse/etc classes with matching decorators (EDIOrderD01BDecorator, EDIOrderD93ADecorator)? Do I need builder objects or can I do: // $myOrder is instance of AOrder $myOrder->toEDIOrder(); $decorator = new EDIOrderD01BDecorator($myOrder); $edi = $decorator->getEDIString(); And it'll have to work the other way around as well. Is the following code a good way of handling this problem or should I go about this differently? $ediString = $myEDIMessageBroker->fetch(); $ediOrderResponse = EDIOrderResponse::fromString($ediString); I'm just not so sure about how I should go about designing the classes and interactions between them. Thanks for reading and helping.

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• UML Diagrams of Multi-Threaded Applications

  - by PersonalNexus

  For single-threaded applications I like to use class diagrams to get an overview of the architecture of that application. This type of diagram, however, hasn’t been very helpful when trying to understand heavily multi-threaded/concurrent applications, for instance because different instances of a class "live" on different threads (meaning accessing an instance is save only from the one thread it lives on). Consequently, associations between classes don’t necessarily mean that I can call methods on those objects, but instead I have to make that call on the target object's thread. Most literature I have dug up on the topic such as Designing Concurrent, Distributed, and Real-Time Applications with UML by Hassan Gomaa had some nice ideas, such as drawing thread boundaries into object diagrams, but overall seemed a bit too academic and wordy to be really useful. I don’t want to use these diagrams as a high-level view of the problem domain, but rather as a detailed description of my classes/objects, their interactions and the limitations due to thread-boundaries I mentioned above. I would therefore like to know: What types of diagrams have you found to be most helpful in understanding multi-threaded applications? Are there any extensions to classic UML that take into account the peculiarities of multi-threaded applications, e.g. through annotations illustrating that some objects might live in a certain thread while others have no thread-affinity; some fields of an object may be read from any thread, but written to only from one; some methods are synchronous and return a result while others are asynchronous that get requests queued up and return results for instance via a callback on a different thread.

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• Class Design for special business rules

  - by Samuel Front

  I'm developing an application that allows people to place custom manufacturing orders. However, while most require similar paperwork, some of them have custom paperwork that only they require. My current class design has a Manufacturer class, of which of one of the member variables is an array of RequiredSubmission objects. However, there are two issues that I am somewhat concerned about. First, some manufacturers are willing to accept either a standard form or their own custom form. I'm thinking of storing this in the RequiredSubmission object, with an array of alternate forms that are a valid substitute. I'm not sure that this is ideal, however. The major issue, however, is that some manufacturers have deadline cycles. For example, forms A, B and C have to be delivered by January 1, while payment must be rendered by January 10. If you miss those, you'll have to wait until the next cycle. I'm not exactly sure how I can get this to work with my existing classes—how can I say "this set of dates all belong to the same cycle, with date A for form A, date B for form B, etc." I would greatly appreciate any insights on how to best design these classes.

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• When do domain concepts become application constructs?

  - by Noren

  I recently posted a question regarding recovering a DDD architecture that became an anemic domain model into a multitier architecture and this question is a follow-on of sorts. My question is when do domain concepts become application constructs. My application is a local client C# 4/WPF with the following architecture: Presentation Layer Views ViewModels Business Layer ??? Domain Layer Classes that take the POCOs with primitive types and create domain concepts (e.g. image, layer, etc) Sanity checks values (e.g. image width 0) Interfaces for DTOs Interface for a repository that abstracts the filesystem Data Access Layer Classes that parse the proprietary binary files into POCOs with primitive types by explicit knowledge of the file format Implementation of domain DTOs Implementation of domain repository class Local Filesystem Proprietary binary files When does the MyImageType domain class with Int32 width, height, and Int32[] pixels become a System.Windows.Media.ImageDrawing? If I put it in the domain layer, it seems like implemenation details are being leaked (what if I didn't want to use WPF?). If I put it in the presentation layer, it seems like it's doing too much. If I create a business layer, it seems like it would be doing too little since there are few "rules" given the CRUD nature of the application. I think all of my reading has lead to analysis paralysis, so I thought fresh eyes might lend some perspective.

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• Using MVC with a retained mode renderer

  - by David Gouveia

  I am using a retained mode renderer similar to the display lists in Flash. In other words, I have a scene graph data structure called the Stage to which I add the graphical primitives I would like to see rendered, such as images, animations, text. For simplicity I'll refer to them as Sprites. Now I'm implementing an architecture which is becoming very similar to MVC, but I feel that that instead of having to create View classes, that the sprites already behave pretty much like Views (except for not being explicitly connected to the Model). And since the Model is only changed through the Controller, I could simply update the view together with the Model in the controller, as in the example below: Example 1 class Controller { Model model; Sprite view; void TeleportTo(Vector2 position) { model.Position = view.Position = position; } } The alternative, I think, would be to create View classes that wrap the sprites, make the model observable, and make the view react to changes on the model. This seems like a lot of extra work and boilerplate code, and I'm not seeing the benefits if I'm just going to have one view per controller. Example 2 class Controller { Model model; View view; void TeleportTo(Vector2 position) { model.Position = position; } } class View { Model model; Sprite sprite; View() { model.PropertyChanged += UpdateView; } void UpdateView() { sprite.Position = model.Position; } } So, how is MVC or more specifically, the View, usually implemented when using a retained-mode renderer? And is there any reason why I shouldn't stick with example 1?

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• Session serialization in JavaEE environment

  - by Ionut

  Please consider the following scenario: We are working on a JavaEE project for which the scalability starts to become an issue. Up until now, we were able to scale up but this is no longer an option. Therefore we need to consider scaling out and preparing the App for a clustered environment. Our main concern right now is serializing the user sessions. Sadly, we did not consider from the beginning the issue and we are encountering the following excetion: java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: org.apache.catalina.session.StandardSessionFacade I did some research and this exception is thrown because there are objects stored on the session which does not implement the Serializable interface. Considering that all over the app there are quite a few custom objects which are stored on the session without implementing this interface, it would require a lot of tedious work and dedication to fix all these classes declaration. We will fix all this declarations but the main concern is that, in the future, there may be a developer which will add a non Serializable object on the session and break the session serialization & replication over multiple nodes. As a quick overview of the project, we are developing using a home grown framework based on Struts 1 with the Servlet 3.0 API. This means that at this point, we are using the standard session.getAttribute() and session.setAttribute() to work with the session and the session handling is scattered all over the code base. Besides updating the classes of the objects stored on session and making sure that they implement the Serializable interface, what other measures of precaution should we take in order to ensure a reliable Session replication capability on the Application layer? I know it is a little bit late to consider this but what would be the best practice in this case? Furthermore, are there any other issues we should consider regarding this transition? Thank you in advance!

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• MVC and individual elements of the model under a common base class

  - by Stewart

  Admittedly my experience of using the MVC pattern is limited. It might be argued that I don't really separate the V from the C, though I keep the M separate from the VC to the extent I can manage. I'm considering the scenario in which the application's model includes a number of elements that have a common base class. For example, enemy characters in a video game, or shape types in a vector graphics app. The view wants to render these elements. Of course, the different subclasses call for different rendering. The problem is that the elements are part of the model. Rendering them is conceptually part of the view. But how they are to be rendered depends on parameters of both: Attributes and state of the element are parameters of the model User settings are parameters of the view - and to support multiple platforms and/or view modes, different views may be used What's your preferred way of dealing with this? Put the rendering code in the model classes, passing in any view parameters? Put the rendering code in the view, using a switch or similar to select the right rendering for the model element type? Have some intermediate classes as a model-view interface, of which the model will create objects on demand and the view will then render them? Something else?

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• Inspiring the method of teaching. Example- C++ :)

  - by Ashwin

  A year ago I graduated with a degree in Computer Science and Engineering. Considering C++ as the first choice of programming language I have been in the process of learning C++ in many ways. At first - five years back - I had many conceptions, most of which were so abstract to me. It started when I knew almost everything about Structs in C and nothing about Classes in C++. I went through a great time experimenting them all and learning a lot. I had a hard time evaluating Procedural programming vs Object-Oriented Programming. Deciding when to choose Procedural or Object-Oriented Programming took a great deal of patience for me. I knew that I cannot underestimate any of these Programming styles... Though Procedural programming is often a better choice than simple sequential unstructured programming, when solving problems with procedural programming, we usually divide one problem into several steps in order regarded as functions. Then we call these functions one by one to get the result of the problem. When solving problems with Object Oriented Priciples we divide one problem into several classes and form the interaction between them. Evaluating these two at the beginning (as a learner) required a lot of inspiration and thoughts. Instructing to think step by step. Relative concepts to understand deeply. Intensive interests to contrast both solving in both POP and OOP. If you were ever a mentor: What ideas/methods would you teach to students in which it will Inspire them to learn a programming language (in general, computer sciences)?

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• Low-level game engine renderer design

  - by Mark Ingram

  I'm piecing together the beginnings of an extremely basic engine which will let me draw arbitrary objects (SceneObject). I've got to the point where I'm creating a few sensible sounding classes, but as this is my first outing into game engines, I've got the feeling I'm overlooking things. I'm familiar with compartmentalising larger portions of the code so that individual sub-systems don't overly interact with each other, but I'm thinking more of the low-level stuff, starting from vertices working up. So if I have a Vertex class, I can combine that with a list of indices to make a Mesh class. How does the engine determine identical meshes for objects? Or is that left to the level designer? Once we have a Mesh, that can be contained in the SceneObject class. And a list of SceneObject can be placed into the Scene to be drawn. Right now I'm only using OpenGL, but I'm aware that I don't want to be tying OpenGL calls right in to base classes (such as updating the vertices in the Mesh, I don't want to be calling glBufferData etc). Are there any good resources that discuss these issues? Are there any "common" heirachies which should be used?

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• Logistics of code reuse (OOP)

  - by Ominus

  One of the driving points behind OOP is code reuse. I am curious about the actual logistics of this and how others both in team or solo handle it. For example lets say you have 5 projects you have worked on and between them you have a ton of classes that you think would be useful in other projects. How do you store them? Are they just in the normal project repository or do you break out the relevant classes and have them (as now copies) in another unique source repository that only houses code pieces that are intended to be reused? How do you go about finding or even knowing that there is a good piece of code out there that you should reuse? It's easier if your solo because you remember that you have coded something similar but even then it becomes kind of a stretch. If there is some way that you are storing these pieces of code do you then also have them indexed and searchable by tag or something. I fear that it just boils down to some tribal knowledge that you just know that for situation A i need solution B and we have a good piece of code that already can help here. A bit verbose but I hope you get what I am aiming at. If you think of a better way to make the question clearer please have at it :) TIA!

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• Overwhelmed by complex C#/ASP.NET project in Visual Studio 2008

  - by Darren Cook

  I have been hired as a junior programmer to work on projects that extend existing functionality in a very large, complex solution. The code base consists of C#, ASP.NET, jQuery, javascript, html and xml. I have some knowledge of all these in addition to fair knowledge of object-oriented programming and its fundamental concepts of inheritance, abstraction, polymorphism and encapsulation. I can follow code up through its base classes, interfaces, abstract classes and understand a large part of the code that I read while doing this. However, this solution is so humongous and so many things get tied together whenever I navigate through the code that I feel absolutely overwhelmed. I often find myself unable to fully follow everything that is going on with objects being serialized, large amounts of C# and javascript operating on the same pages and methods being called from template files that consist mainly of markup. I love learning about code, but trying to deal with this really stresses me out. Additionally, I do know that a significant amount of unit testing has been done but I know nothing about unit testing or how to utilize it. Any advice anyone could offer me regarding dealing with a large code base while using Visual Studio 2008 would be greatly appreciated. Are there tools that I can use to help get a handle on what is going on? Perhaps there are things even in Visual Studio that I am not aware of. How can I follow the code to low level functionality in order to get a better grasp of what is going on at a high level?

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• Should you create a class within a method?

  - by Amndeep7

  I have made a program using Java that is an implementation of this project: http://nifty.stanford.edu/2009/stone-random-art/sml/index.html. Essentially, you create a mathematical expression and, using the pixel coordinate as input, make a picture. After I initially implemented this in serial, I then implemented it in parallel due to the fact that if the picture size is too large or if the mathematical expression is too complex (especially considering the fact that I made the expression recursively), it takes a really long time. During this process, I realized that I needed two classes which implemented the Runnable interface as I had to put in parameters for the run method, which you aren't allowed to do directly. One of these classes ended up being a medium sized static inner class (not large enough to make an independent class file for it though). The other though, just needed a few parameters to determine some indexes and the size of the for loop that I was making run in parallel - here it is: class DataConversionRunnable implements Runnable { int jj, kk, w; DataConversionRunnable(int column, int matrix, int wid) { jj = column; kk = matrix; w = wid; } public void run() { for(int i = 0; i < w; i++) colorvals[kk][jj][i] = (int) ((raw[kk][jj][i] + 1.0) * 255 / 2.0); increaseCounter(); } } My question is should I make it a static inner class or can I just create it in a method? What is the general programming convention followed in this case?

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• Augmenting functionality of subclasses without code duplication in C++

  - by Rob W

  I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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• Sitecore Item Web API and Json.Net Test Drive (Part II –Strongly Typed)

  - by jonel

  In the earlier post I did related to this topic, I have talked about using Json.Net to consume the result of Sitecore Item Web API. In that post, I have used the keyword dynamic to express my intention of consuming the returned json of the API. In this article, I will create some useful classes to write our implementation of consuming the API using strongly-typed. We will start of with the Record class which will hold the top most elements the API will present us. Pretty straight forward class. It has 2 properties to hold the statuscode and the result elements. If you intend to use a different property name in your class from the json property, you can do so by passing a string literal of the json property name to the JsonProperty attribute and name your class property differently. If you look at the earlier post, you will notice that the API returns an array of items that contains all of the Sitecore content item or items and stores them under the result->items array element. To be able to map that array of items, we have to write a collection property and decorate that with the JsonProperty attribute. The JsonItem class is a simple class which will map to the corresponding item property contained in the array. If you notice, these properties are just the basic Sitecore fields. And here’s the main portion of this post that will binds them all together. And here’s the output of this code. In closing, the same result can be achieved using the dynamic keyword or defining classes to map the json propery returned by the Sitecore Item Web API. With a little bit more of coding, you can take advantage of power of strongly-typed solution. Have a good week ahead of you.

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• Benefits of classic OOP over Go-like language

  - by tylerl

  I've been thinking a lot about language design and what elements would be necessary for an "ideal" programming language, and studying Google's Go has led me to question a lot of otherwise common knowledge. Specifically, Go seems to have all of the interesting benefits from object oriented programming without actually having any of the structure of an object oriented language. There are no classes, only structures; there is no class/structure inheritance -- only structure embedding. There aren't any hierarchies, no parent classes, no explicit interface implementations. Instead, type casting rules are based on a loose system similar to duck-typing, such that if a struct implements the necessary elements of a "Reader" or a "Request" or an "Encoding", then you can cast it and use it as one. Does such a system obsolete the concept of OOP? Or is there something about OOP as implemented in C++ and Java and C# that is inherently more capable, more maintainable, somehow more powerful that you have to give up when moving to a language like Go? What benefit do you have to give up to gain the simplicity that this new paradigm represents?

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• How to implement child-parent aggregation link in C++?

  - by Giorgio

  Suppose that I have three classes P, C1, C2, composition (strong aggregation) relations between P <>- C1 and P <>- C2, i.e. every instance of P contains an instance of C1 and an instance of C2, which are destroyed when the parent P instance is destroyed. an association relation between instances of C1 and C2 (not necessarily between children of the same P). To implement this, in C++ I normally define three classes P, C1, C2, define two member variables of P of type boost::shared_ptr<C1>, boost::shared_ptr<C2>, and initialize them with newly created objects in P's constructor, implement the relation between C1 and C2 using a boost::weak_ptr<C2> member variable in C1 and a boost::weak_ptr<C1> member variable in C2 that can be set later via appropriate methods, when the relation is established. Now, I also would like to have a link from each C1 and C2 object to its P parent object. What is a good way to implement this? My current idea is to use a simple constant raw pointer (P * const) that is set from the constructor of P (which, in turn, calls the constructors of C1 and C2), i.e. something like: class C1 { public: C1(P * const p, ...) : paren(p) { ... } private: P * const parent; ... }; class P { public: P(...) : childC1(new C1(this, ...)) ... { ... } private: boost::shared_ptr<C1> childC1; ... }; Honestly I see no risk in using a private constant raw pointer in this way but I know that raw pointers are often frowned upon in C++ so I was wondering if there is an alternative solution.

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• Everything has an Interface [closed]

  - by Shane

  Possible Duplicate: Do I need to use an interface when only one class will ever implement it? I am taking over a project where every single real class is implementing an Interface. The vast majority of these interfaces are implemented by a single class that share a similar name and the exact same methods (ex: MyCar and MyCarImpl). Almost no 2 classes in the project implement more than the interface that shares its name. I know the general recommendation is to code to an interface rather than an implementation, but isn't this taking it a bit too far? The system might be more flexible in that it is easier to add a new class that behaves very much like an existing class. However, it is significantly harder to parse through the code and method changes now require 2 edits instead of 1. Personally, I normally only create interfaces when there is a need for multiple classes to have the same behavior. I subscribe to YAGNI, so I don't create something unless I see a real need for it. Am I doing it all wrong or is this project going way overboard?

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• Can't run minecraft on ubuntu 12.04 lts [duplicate]

  - by user170011

  This question already has an answer here: How to correctly install and troubleshoot Minecraft (Client) 3 answers I was trying to run minecraft on my laptop with ubuntu 12.04 lts 64 bit. I have a lenovo ideapad p580 with 7.7 Gb and an Intel® Core™ i7-3520M CPU @ 2.90GHz × 4 processor. Under the graphics section of the system overview in ubuntu it says I have none installed. My computer comes with and nvidia geforce graphics card but it isnt recognized. When I start minecraft I get this crash report. ---- Minecraft Crash Report ---- // Shall we play a game? Time: 24/06/13 7:23 PM Description: Failed to start game org.lwjgl.LWJGLException: Could not init GLX at org.lwjgl.opengl.LinuxDisplayPeerInfo.initDefaultPeerInfo(Native Method) at org.lwjgl.opengl.LinuxDisplayPeerInfo.<init>(LinuxDisplayPeerInfo.java:52) at org.lwjgl.opengl.LinuxDisplay.createPeerInfo(LinuxDisplay.java:684) at org.lwjgl.opengl.Display.create(Display.java:854) at org.lwjgl.opengl.Display.create(Display.java:784) at org.lwjgl.opengl.Display.create(Display.java:765) at net.minecraft.client.Minecraft.a(SourceFile:235) at avv.a(SourceFile:56) at net.minecraft.client.Minecraft.run(SourceFile:507) at java.lang.Thread.run(Thread.java:679) A detailed walkthrough of the error, its code path and all known details is as follows: -- System Details -- Details: Minecraft Version: 1.5.2 Operating System: Linux (amd64) version 3.5.0-34-generic Java Version: 1.6.0_27, Sun Microsystems Inc. Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Sun Microsystems Inc. Memory: 406175448 bytes (387 MB) / 514523136 bytes (490 MB) up to 1908932608 bytes (1820 MB) JVM Flags: 2 total; -Xmx2048M -Xms512M AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used Suspicious classes: No suspicious classes found. IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0 LWJGL: 2.4.2 OpenGL: ~~ERROR~~ NullPointerException: null Is Modded: Probably not. Jar signature remains and client brand is untouched. Type: Client (map_client.txt) Texture Pack: Default Profiler Position: N/A (disabled) Vec3 Pool Size: ~~ERROR~~ NullPointerException: null I can run it on different versions of linux such as fedora.

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• Do you leverage the benefits of the open-closed principle?

  - by Kaleb Pederson

  The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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• Object oriented wrapper around a dll

  - by Tom Davies

  So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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• Class Design - Space Simulator

  - by Peteyslatts

  I have pretty much taught myself everything I know about programming, so while I know how to teach myself (books, internet and reading API's), I'm finding that there hasn't been a whole lot in the way of good programming. So I have two questions: First the broad one: Does anyone have suggestions as to sources for learning about good programming habits and techniques? I'd prefer it if the resource wasn't a 5000 page tome. The more I can read it in installments the better. More specifically: I am finishing up learning the basics of XNA and I want to create a space simulator to test my knowledge. This isn't a full scale simulator, but just something that covers everything I learned. It's also going to be modular so I can build on it, after I get the basics down. One of the early features I want to implement is AI. And I want to take this into account as I'm designing my classes so I can minimize rewriting code. So my question: How should I design ship classes so that both the player and AI can use them? The only idea I have so far is: Create a ship class that contains stats, models, textures, collision data etc. The player and AI would then have the data for position, rotation, health, etc and would base their status off of the ship stats.

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