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• Is this bad Object Oriented Design? (derived class used in base class)

  - by Earlz

  Hello, Can someone tell me if this class structure is bad? class abstract Parent{ public Child Foo(){ return new Child(); } } class Child : Parent{} I've heard that referring to a derived type from a base type is always bad and signs of bad design. Can someone tell me why this is bad or even if it is bad?

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• "Circuit breaker" for net.msmq?

  - by Alex

  Hi, The Circuit Breaker pattern, from the book Release It!, protects a service from requests while it is failing (or recovering). The net.msmq binding used with transactions give us nice retry and poison message capabilities. But I am missing the implementation of such a "Circuit breaker" pattern. A service is put under even heavier load by retries while it is already in a failure condition (like DB connectivity issues causing loads of blocked threads etc.). Anyone knows about a behavior extension or similar that explicitly closes the service host when defined failure thresholds have been exceeded? Cheers, Alex

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• Python and the Singleton Pattern

  - by dmanxiii

  What is the best way to implement the singleton pattern in Python? It seems impossible to declare the constructor private or protected as is normally done with the Singleton pattern...

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• P/Invoke or C++/CLI for wrapping a C library

  - by Ian G

  Have a moderate size (40-odd function) C API that needs to be called from a C# project. The functions logically break up to form a few classes that will be API presented to the rest of the project. Are there any objective reasons to prefer P/Invoke or C++/CLI for the interoperability underneath that API, in terms of robustness, maintainability, deployment, ...? The issues I could think of that might be, but aren't problematic are: C++/CLI will require an separate assembly, the P/Invoke classes can be in the main assembly. (We've already got multiple assemblies and there'll be the C dlls anyway so not a major issue). Performance doesn't seem differ noticeable between the two methods. Issues that I'm not sure about are: My feeling is C++/CLI will be easier to debug if there's inter-op problem, is this true? Language familiarity enough people know C# and C++ but knowledge of details of C++/CLI are rarer here. Anything else?

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• Facade controller, is it efficient?

  - by Berlioz

  Using a facade controller pattern in .net. It seems as if though it is not efficient BECAUSE, for every event that happens in a domain object(Sales, Register, Schedule, Car) it has to be subscribed to by the controller(use case controller) and then the controller in turn has to duplicate that same event to make it available for the presentation, so that the presentation can show it to the user. Does this make sense? Please comment!

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• C# event or delegate or other solution?

  - by user295734

  Looking for some help or programmng ideas or mayeb there is some pattern that would help. Have an application that needs to fire alot of events sequentially, it could up to 100 or more unique events, it will be dynamic depeneding on the situation. Trying to find the best practice for doing this. My main idea right now is to create a list of objects iterate thru them, and fire each event. This seems wrong, or bad practice. Or maybe have one object and pass a list or params into one event? Or am I missing some feature in .NET that i could be using or implementing?

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• How should Application.Run() be called for the main presenter a MVP WinForms app?

  - by Mr Roys

  I'm learning to apply MVP to a simple WinForms app (only one form) in C# and encountered an issue while creating the main presenter in static void Main(). Is it a good idea to expose a View from the Presenter in order to supply it as a parameter to Application.Run()? Currently, I've implemented an approach which allows me to not expose the View as a property of Presenter: static void Main() { IView view = new View(); Model model = new Model(); Presenter presenter = new Presenter(view, model); presenter.Start(); Application.Run(); } The Start and Stop methods in Presenter: public void Start() { view.Start(); } public void Stop() { view.Stop(); } The Start and Stop methods in View (a Windows Form): public void Start() { this.Show(); } public void Stop() { // only way to close a message loop called // via Application.Run(); without a Form parameter Application.Exit(); } The Application.Exit() call seems like an inelegant way to close the Form (and the application). The other alternative would be to expose the View as a public property of the Presenter in order to call Application.Run() with a Form parameter. static void Main() { IView view = new View(); Model model = new Model(); Presenter presenter = new Presenter(view, model); Application.Run(presenter.View); } The Start and Stop methods in Presenter remain the same. An additional property is added to return the View as a Form: public void Start() { view.Start(); } public void Stop() { view.Stop(); } // New property to return view as a Form for Application.Run(Form form); public System.Windows.Form View { get { return view as Form(); } } The Start and Stop methods in View (a Windows Form) would then be written as below: public void Start() { this.Show(); } public void Stop() { this.Close(); } Could anyone suggest which is the better approach and why? Or there even better ways to resolve this issue?

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• TDD - beginner problems and stumbling blocks

  - by Noufal Ibrahim

  While I've written unit tests for most of the code I've done, I only recently got my hands on a copy of TDD by example by Kent Beck. I have always regretted certain design decisions I made since they prevented the application from being 'testable'. I read through the book and while some of it looks alien, I felt that I could manage it and decided to try it out on my current project which is basically a client/server system where the two pieces communicate via. USB. One on the gadget and the other on the host. The application is in Python. I started off and very soon got entangled in a mess of rewrites and tiny tests which I later figured didn't really test anything. I threw away most of them and and now have a working application for which the tests have all coagulated into just 2. Based on my experiences, I have a few questions which I'd like to ask. I gained some information from http://stackoverflow.com/questions/1146218/new-to-tdd-are-there-sample-applications-with-tests-to-show-how-to-do-tdd but have some specific questions which I'd like answers to/discussion on. Kent Beck uses a list which he adds to and strikes out from to guide the development process. How do you make such a list? I initially had a few items like "server should start up", "server should abort if channel is not available" etc. but they got mixed and finally now, it's just something like "client should be able to connect to server" (which subsumed server startup etc.). How do you handle rewrites? I initially selected a half duplex system based on named pipes so that I could develop the application logic on my own machine and then later add the USB communication part. It them moved to become a socket based thing and then moved from using raw sockets to using the Python SocketServer module. Each time things changed, I found that I had to rewrite considerable parts of the tests which was annoying. I'd figured that the tests would be a somewhat invariable guide during my development. They just felt like more code to handle. I needed a client and a server to communicate through the channel to test either side. I could mock one of the sides to test the other but then the whole channel wouldn't be tested and I worry that I'd miss that. This detracted from the whole red/green/refactor rhythm. Is this just lack of experience or am I doing something wrong? The "Fake it till you make it" left me with a lot of messy code that I later spent a lot of time to refactor and clean up. Is this the way things work? At the end of the session, I now have my client and server running with around 3 or 4 unit tests. It took me around a week to do it. I think I could have done it in a day if I were using the unit tests after code way. I fail to see the gain. I'm looking for comments and advice from people who have implemented large non trivial projects completely (or almost completely) using this methodology. It makes sense to me to follow the way after I have something already running and want to add a new feature but doing it from scratch seems to tiresome and not worth the effort. P.S. : Please let me know if this should be community wiki and I'll mark it like that. Update 0 : All the answers were equally helpful. I picked the one I did because it resonated with my experiences the most. Update 1: Practice Practice Practice!

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• View artifacts leaking into the model of MVC

  - by Jono

  In an ASP.NET MVC application (which has very little chance of having its view technology ported to something non-HTML, but whose functional requirements evolve weekly,) how much HTML should ideally be allowed to be directly represented in the Model? I might come across as a design bigot for this, but I regard it as bad practice to allow any view constructs to "leak" into the model in an MVC application (and vice versa). For example, a Model that represents an item you're about to purchase should know nothing about the HTML check box that says "add giftwrap/message", nor should it know about any HTML drop down lists for payment card types. Conversely the View shouldn't be doing work like figuring out button text by translating keys into values (by looking in resource files.)

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• Should my internal API classes be all in one package?

  - by Chris

  I'm hard at work packaging up an API for public consumption. As such I'm trying to limit the methods that are exposed to only those that I wish to be public and supportable. Underneath this of course there are a multitude of limited access methods. The trouble is that I have a lot of internal code that needs to access these restricted methods without making those methods public. This creates two issues: I can't create interfaces to communicate between classes as this would make these my internal methods public. I can't access protected or default methods unless I put the majority of my internal classes in the same package. So, I have around 70 or 80 internal classes in cleanly segregated packages BUT with overly permissive access modifiers. Would you say that a single package is the lesser of two evils or is there a better way to be able to mask my internal methods whilst keeping more granular packages? I'd be interested to find out the best practice here. I'm already aware of This

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• How to best launch C++ application from web page

  - by JB

  I guess there are two parts to this question, one technical and one best practice for security and doing things "right". I'm working on a little game using C++ / directx but I would like to be able to launch it from a web page by someone clicking on a link on that page. Ideally I would like the first time they clicked for it to launch an installer downloads and installs the game on their machine, and then the next time to launch an application which updates the game from a web site if it's old and then launches it. I have no problems with the expected security popups and questions the first time it runs. I want people to be certain what they are installing and understand what they are doing. But it would be nice if once it is installed they could run it with the minimum of fuss. My question then is what technologies I could use to do this? I'm thinking that it would need a browser plugin and an activex control so that first time you'd install that, and subsequently the control/plugin would be able to launch the game. I'm not sure that under newer browser secuity models that a plugin would have the permissions to be able to run an installer though or silently invoke applications on the client machine even if they are already installed. Is there a more sensible way to achive what I want to achieve? And I'm worried about the security aspects too. I want this to be convenient for users but I of course want to do it "right". I know this can be done as I've seen several mmorpg type games that launch in this way from the browser now but it's not entirely clear to me how they've done it.

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• .NET without use of DLL's

  - by Kieran

  Hi SO community I have been issued a problem with security. A bank will not allow use of DLL's in the project. What sort of structure would be needed to allow DataAccess and or the use of external services (like an email client mailchimp, icontct). has anyone else encountered this sort of problem before? If they have how should the project be structured (.net 3.5+). Thanks, KJ

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• Import RSS feed into a Typo3 template

  - by Kaaviar

  Hi, I'm a total beginner with Typo3 and would like to show a RSS feed in a Typo3 template using typoscript. And I have no idea how to do this ! Is there any way to do this quite easily ? Calling an external PHP script maybe ? Thx !

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• A good approach to db planing for reporting service

  - by Itay Moav

  The scenario: Big system (~200 tables). 60,000 users. Complex reports that will require me to do multiple queries for each report and even those will be complex queries with inner queries all over the place + some processing in PHP. I have seen an approach, which I am not sure about: Having one centralized, de-normalized, table that registers any activity in the system which is reportable. This table will hold mostly foreign keys, so she should be fairly compact and fast. So, for example (My system is a virtual learning management system), A user enrolls to course, the table stores the user id, date, course id, organization id, activity type (enrollment). Of course I also store this data in a normalized DB, which the actual application uses. Pros I see: easy, maintainable queries and code to process data and fast retrieval. Cons: there is a danger of the de-normalized table to be out of sync with the real DB. Is this approach worth considering, or (preferably from experience) is total $#%#%t?

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• c# object initializer complexity. best practice

  - by Andrew Florko

  I was too excited when object initializer appeared in C#. MyClass a = new MyClass(); a.Field1 = Value1; a.Field2 = Value2; can be rewritten shorter: MyClass a = new MyClass { Field1 = Value1, Field2 = Value2 } Object initializer code is more obvious but when properties number come to dozen and some of the assignment deals with nullable values it's hard to debug where the "null reference error" is. Studio shows the whole object initializer as error point. Nowadays I use object initializer for straightforward assignment only for error-free properties. How do you use object initializer for complex assignment or it's a bad practice to use dozen of assigments at all? Thank you in advance!

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• C++ : Efficient code

  - by Alerty

  What code sample is a brilliant example of efficiency in the C++ programming language and its features?

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• Which design pattern is most appropriate?

  - by Anon

  Hello, I want to create a class that can use one of four algorithms (and the algorithm to use is only known at run-time). I was thinking that the Strategy design pattern sounds appropriate, but my problem is that each algorithm requires slightly different parameters. Would it be a bad design to use strategy, but pass in the relevant parameters into the constructor?. Here is an example (for simplicity, let's say there are only two possible algorithms) ... class Foo { private: // At run-time the correct algorithm is used, e.g. a = new Algorithm1(1); AlgorithmInterface* a; }; class AlgorithmInterface { public: virtual void DoSomething = 0; }; class Algorithm1 : public AlgorithmInterface { public: Algorithm1( int i ) : value(i) {} virtual void DoSomething(){ // Does something with int value }; int value; }; class Algorithm2 : public AlgorithmInterface { public: Algorithm2( bool b ) : value(b) {} virtual void DoSomething(){ // Do something with bool value }; bool value; };

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• What are possible designs for the DCI architecture?

  - by Gabriel Šcerbák

  What are possibles designs for implementation of the DCI (data, contexts, interactions) architecture in different OOP languages? I thought of Policy based design (Andrei Alexandrescu) for C++, DI and AOP for Java. However, I also thought about using State design pattern for representing roles and some sort of Template method for the interactions... What are the other possibilities?

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• c++ Design pattern for CoW, inherited classes, and variable shared data?

  - by krunk

  I've designed a copy-on-write base class. The class holds the default set of data needed by all children in a shared data model/CoW model. The derived classes also have data that only pertains to them, but should be CoW between other instances of that derived class. I'm looking for a clean way to implement this. If I had a base class FooInterface with shared data FooDataPrivate and a derived object FooDerived. I could create a FooDerivedDataPrivate. The underlying data structure would not effect the exposed getters/setters API, so it's not about how a user interfaces with the objects. I'm just wondering if this is a typical MO for such cases or if there's a better/cleaner way? What peeks my interest, is I see the potential of inheritance between the the private data classes. E.g. FooDerivedDataPrivate : public FooDataPrivate, but I'm not seeing a way to take advantage of that polymorphism in my derived classes. class FooDataPrivate { public: Ref ref; // atomic reference counting object int a; int b; int c; }; class FooInterface { public: // constructors and such // .... // methods are implemented to be copy on write. void setA(int val); void setB(int val); void setC(int val); // copy constructors, destructors, etc. all CoW friendly private: FooDataPrivate *data; }; class FooDerived : public FooInterface { public: FooDerived() : FooInterface() {} private: // need more shared data for FooDerived // this is the ???, how is this best done cleanly? };

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• Is there a design pattern for injecting methods into a class?

  - by glenn I.

  I have a set of classes that work together (I'm coding in javascript). There is one parent class and a number of child classes that are instantiated by the parent class. I have a number of clients of these classes that each need to add on one more methods to the parent or child classes. Rather than having each client inherit from these classes, which is doable but messy because of the child classes, I am having these clients pass functions into the parent class when they instantiate the main class. The main class creates the methods dynamically and the clients can call the methods like they were there all along. My questions are: is this a sensible thing to do? what would the design pattern be for what I am doing?

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• Python's JSON module doesn't use __get__?

  - by Matt

  When I serialize a list of objects with a custom __get__ method, __get__ is not called and the raw (unprocessed by custom __get__) value from __set__ is used. How does Python's json module iterate over an item? Note: if I iterate over the list before serializing, the correct value returned by __get__ is used.

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• What is the MVC equivalent of this code:

  - by Ian Boyd

  Here's the easy pseudo-code: void TextBox1Changed() { //If the text isn't a number, color it red if (!IsValidNumber(TextBox1.Text) TextBox1.Color = Pink; else TextBox1.Color = WindowColor; } What's the MVC enterprisey version?

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• QuestionOrAnswer model?

  - by Mark

  My site has Listings. Users can ask Questions about listings, and the author of the listing can respond with an Answer. However, the Answer might need clarification, so I've made them recursive (you can "answer" an answer). So how do I set up the database? The way I have it now looks like this (in Django-style models): class QuestionOrAnswer(Model): user = ForeignKey(User, related_name='questions') listing = ForeignKey(Listing, related_name='questions') parent = models.ForeignKey('self', null=True, blank=True, related_name='children') message = TextField() But what bugs me is that listing is now an attribute of the answers as well (it doesn't need to be). What happens if the database gets mangled and an answer belongs to a different listing than its parent question? That just doesn't make any sense. We can separate it with polymorphism: QuestionOrAnswer user message created updated Question(QuestionOrAnswer) shipment Answer(QuestionOrAnswer) parent = ForeignKey(QuestionOrAnswer) And that ought to work, but now ever question and answer is split into 2 tables. Is it worth this overhead for clearly defined models?

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• How could it happen that version control software emerged so lately?

  - by sharptooth

  According to Wikipedia (the table at the page bottom), the earliest known version control systems were CVS and TeamWare both known from year 1990. How can it be? Software development has been here from at most 1960's and I honestly can't imagine working with codebase without version control. How could it happen that version control software emerged so lately compared to software development?

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• paged list with checkboxes, keep the checkbox value browsing through the paging?

  - by Dejan.S

  Hi. I got a list of customers I thought I would list in a gridview or a repeater with customer html, it gone have paging. I'm gone have a checkbox for each customer in the list. Do you guys have any suggestions on how I should do to keep the checkbox value when I go to page 2-3-4 ect in the paging. I'm thinking a session to store the id of the checked customers. After I'm done setting the values they go to the database. Do you got any other ideas then the session I'm thinking of? thanks guys

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