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  • Generic Abstract Singleton with Custom Constructor in C#

    - by Heka
    I want to write a generic singleton with an external constructor. In other words the constructor can be modified. I have 2 designs in my mind but I don't know whether they are practical or not. First one is to enforce derived class' constructor to be non-public but I do not know if there is a way of it? Second one is to use a delegate and call it inside the constructor? It isn't necessarily to be a constructor. The reason I chose custom constructor is doing some custom initializations. Any suggestions would be appreciated :)

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  • Factory vs instance constructors

    - by Neil N
    I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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  • C++ abstract class template + type-specific subclass = trouble with linker

    - by user333279
    Hi there, The project in question is about different endpoints communicating with each other. An endpoint sends events (beyond the scope of the current problem) and can process incoming events. Each event is represented in a generic object as follows: #pragma interface ... // some includes template<typename T> class Event { public: Event(int senderId, Type type, T payload); // Type is an enum Event(int senderId, Type type, int priority, T payload); virtual ~Event(); virtual int getSenderId(); virtual int getPriority(); virtual T getPayload(); void setPriority(const int priority); protected: const int senderId; const Type type; const T payload; int priority; }; It has its implementing class with #pragma implementation tag. An endpoint is defined as follows: #pragma interface #include "Event.h" template<typename T> class AbstractEndPoint { public: AbstractEndPoint(int id); virtual ~AbstractEndPoint(); virtual int getId(); virtual void processEvent(Event<T> event) = 0; protected: const int id; }; It has its implementing class too, but only the constructor, destructor and getId() are defined. The idea is to create concrete endpoints for each different payload type. Therefore I have different payload objects and specific event classes for each type, e.g. Event<TelegramFormatA>, Event<TelegramFormatB> and ConcreteEndPoint for TelegramFormatA, ConcreteEndPoint for TelegramFormatB respectively. The latter classes are defined as class ConcreteEndPoint : AbstractEndPoint<TelegramFormatA> { ... } I'm using g++ 4.4.3 and ld 2.19. Everything compiles nicely, but the linker complaints about undefined references to type-specific event classes, like Event<TelegramFormatA>::Event(....) . I tried explicit instantiation using template class AbstractEndPoint<TelegramFormatA>; but couldn't get past the aforementioned linker errors. Any ideas would be appreciated.

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  • Identifying a class which is extending an abstract class

    - by Simon A. Eugster
    Good Evening, I'm doing a major refactoring of http://wiki2xhtml.sourceforge.net/ to finally get better overview and maintainability. (I started the project when I decided to start programming, so – you get it, right? ;)) At the moment I wonder how to solve the problem I'll describe now: Every file will be put through several parsers (like one for links, one for tables, one for images, etc.): public class WikiLinks extends WikiTask { ... } public class WikiTables extends WikiTask { ... } The files will then be parsed about this way: public void parse() { if (!parse) return; WikiTask task = new WikiLinks(); do { task.parse(this); } while ((task = task.nextTask()) != null); } Sometimes I may want to use no parser at all (for files that only need to be copied), or only a chosen one (e.g. for testing purposes). So before running task.parse() I need to check whether this certain parser is actually necessary/desired. (Perhaps via Blacklist or Whitelist.) What would you suggest for comparing? An ID for each WikiTask (how to do?)? Comparing the task Object itself against a new instance of a WikiTask (overhead)?

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  • Formal name of Magento’s Class Override Design Pattern?

    - by Alan Storm
    Magento is a newish (past 5 years) PHP based Ecommerce system with an architecture that's similar to the Java Spring framework (or so I've been told) One of the features of the Framework is certain classes are not directly instantiated. Rather than do something like $model = new Mage_Foo_Model_Name(); you pass an identifier into a static method on a global application object $model = Mage::getModel('foo/name'); and this instantiates the class for you. One of the wins with this approach is getModel checks a global configuration system for the foo/name identifier, and instantiates the class name it finds in the configuration system. This allows you to change the behavior of a Model system wide with a single configuration change. Is there a formal, Gang of Four or otherwise, name that describes this system/design pattern? The instantiation itself looks like a classic Factory pattern, but I'm specifically interested in the whole "override a class in the system via configuration" aspect. Is there a name/concept that covers this, or is it contained within the worldview of a Factory?

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  • An RMIPRoxyFactoryBean factory in Spring?

    - by Robert Munteanu
    I'm currently using a Spring RmiProxyFactoryBean to access remote services. Since requirements have changed, I need to specify at runtime a different host - there can be many of them - , but the remoteServiceInterface and the non-host components of the remoteServiceUrl remain the same. Conceptually speaking, I'd see a bean definition similar to: <bean class="org.springframework.remoting.rmi.RmiProxyFactoryBeanFactory"> <property name="serviceInterface" value="xxx"/> <property name="serviceUrl" value="rmi://#{HOST}:1099/ServiceUrl"/> </bean> which exposes a Object getServiceFor(String hostName); Is there such a service available with Spring? Alternatively, do you see another way of doing this? Please note that the host list will not be known at compile or startup time, so I can't generate it in the xml file.

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  • Abstract over X

    - by Bruno Bieth
    Sorry for this english related question but I only came across that expression in the context of IT. What does abstracting over something mean ? For example abstracting over objects or abstracting over classes. Thanks

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  • [[alloc] init] as a factory method

    - by iter
    I want to initialize an instance of one of the subclasses of a superclass depending on the arguments to init: [[Vehicle alloc] initWithItinerary: shortWay]; // returns a bicycle [[Vehicle alloc] initWithItinerary: longWay]; // returns a car I can't find examples of code like this. I wonder if this is not idiomatic in Objective C, or I simply am not looking in the right places.

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  • Compiler error when using abstract types

    - by Dylan
    I'm trying to implement a "protocol helper" trait that is responsible for matching up Prompts and Responses. The eventual goal is to have an object that defines the various Prompt and Response classes as subclasses of a sealed trait, then have a class that mixes in the ProtocolSupport trait for that Protocol object. The problem is that my current approach won't compile, even though I'm fairly sure it should. Here's a distilled version of what I've got: trait Protocol { type Response type Prompt <: BasePrompt trait BasePrompt { type Data def validate(response: Response): Validated[Data] } } trait ProtocolSupport[P <: Protocol] { def foo(prompt: P#Prompt, response: P#Response) = { // compiler error prompt.validate(response) } } The compiler doesn't like the response as an argument to prompt.validate: [error] found : response.type (with underlying type P#Response) [error] required: _4.Response where val _4: P [error] prompt.validate(response) [error] ^ This isn't very helpful.. it seems to say that it wants a P.Response but that's exactly what I'm giving it, so what's the problem?

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  • Using antlr and the DLR together -- AST conversion

    - by RCIX
    I have an AST generated via ANTLR, and I need to convert it to a DLR-compatible one (Expression Trees). However, it would seem that i can't use tree pattern matchers for this as expression trees need their subtrees at instantiation (which i can't get). What solution would be best for me to use?

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  • PHP regex to search across multiple lines

    - by Gaz
    I'm using preg_* in PHP to search for the pattern <!-- %{data=THIS GETS MATCHED}% --> and pull out the matched text. The pattern for this is: preg_match('#<!-- %{' . $knownString . '\s*=\s*(.*?)}% -->#', ...) What I would like it to do is search across multiple lines for the string. For example: <!-- %{data= THIS GETS MATCHED AND RETURNED }% --> How can I edit my current pattern to have this search ability?

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  • Using Nearest Neighbour Algorithm for image pattern recognition

    - by user293895
    So I want to be able to recognise patterns in images (such as a number 4), I have been reading about different algorithms and I would really like to use the Nearest Neighbour algorithm, it looks simple and I do understand it based on this tutorial: http://people.revoledu.com/kardi/tutorial/KNN/KNN_Numerical-example.html Problem is, although I understand how to use it to fill in missing data sets, I don't understand how I could use it as a pattern recognition tool to aim in Image Shape Recognition. Could someone please shed some light as to how this algorithm could work for pattern recognition? I have seen tutorials using OpenCV, however I don't really want to use this library as I have the ability to do the pre-processing myself, and it seems silly that I would implement this library just for what should be a simple nearest neighbour algorithm.

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  • JavaScript/Dojo Module Pattern - how to debug?

    - by djna
    I'm working with Dojo and using the "Module Pattern" as described in Mastering Dojo. So far as I can see this pattern is a general, and widely used, JavaScript pattern. My question is: How do we debug our modules? So far I've not been able to persuade Firebug to show me the source of my module. Firebug seems to show only the dojo eval statement used to execute the factory method. Hence I'm not able to step through my module source. I've tried putting "debugger" statements in my module code, and Firebug seems to halt correctly, but does not show the source. Contrived example code below. This is just an example of sufficient complexity to make the need for debugging plausible, it's not intended to be useful code. The page <!-- Experiments with Debugging --> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>console me</title> <style type="text/css"> @import "../dojoroot/dojo/resources/dojo.css"; @import "../dojoroot/dijit/themes/tundra/tundra.css"; @import "edf.css"; </style> <script type="text/javascript" src="../dojoroot/dojo/dojo.js"> </script> <script type="text/javascript" > dojo.registerModulePath("mytest", "../../mytest"); dojo.require("mytest.example"); dojo.addOnLoad(function(){ mytest.example.greet(); }); </script> </head> <body class="tundra"> <div id="bulletin"> <p>Just Testing</p> </div> </body> </html> <!-- END: snip1 --> The java script I'd like to debug dojo.provide("mytest.example"); dojo.require("dijit.layout.ContentPane"); /** * define module */ (function(){ //define the main program functions... var example= mytest.example; example.greet= function(args) { var bulletin = dojo.byId("bulletin"); console.log("bulletin:" + bulletin); if ( bulletin) { var content = new dijit.layout.ContentPane({ id: "dummy", region: "center" }); content.setContent('Greetings!'); dojo._destroyElement(bulletin); dojo.place(content.domNode, dojo.body(), "first"); console.log("greeting done"); } else { console.error("no bulletin board"); } } })();

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  • C# threading pattern that will let me flush

    - by Jeff Alexander
    I have a class that implements the Begin/End Invocation pattern where I initially used ThreadPool.QueueUserWorkItem() to do thread my work. I now have the side effect where someone using my class is calling the Begin (with callback) a ton of times to do a lot of processing so ThreadPool.QueueUserWorkItem is creating a ton of threads to do the processing. That in itself isn't bad but there are instances where they want to abandon the processing and start a new process but they are forced to wait for their first request to finish. Since ThreadPool.QueueUseWorkItem() doesn't allow me to cancel the threads I am trying to come up with a better way to queue up the work and maybe use an explicit FlushQueue() method in my class to allow the caller to abandon work in my queue. Anyone have any suggestion on a threading pattern that fits my needs?

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  • Is Microformat's date-value-pattern fully accessible?

    - by Stephen
    Has there been an announcement (outside microformats.org) that the value-class-pattern is fully accessible? e.g. given <abbr class="value" title="2008-06-24">this Tuesday</abbr>, will a screen reader say "24 June 2008" or will it say "2008 dash 6 dash 24"? History Microformats came along, and were great, except that dates etc were stored in abbr tags: <abbr class="dtstart" title="20070312T1700-06"> March 12, 2007 at 5 PM, Central Standard Time </abbr>` This lead to screen readers doing ridiculous things as noted in hAccessibility. Now that microformats.org have released the value-class-pattern it's a lot better. But I'm left unable to find a declaration from WaSP (or another accessibility source not directly tied to microformats) that declaratively states that they are now accessible to screen readers etc.

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  • Winforms Which Design Pattern / Agile Methodology to choose

    - by ZedBee
    I have developed desktop (winforms) applications without following any proper design pattern or agile methodologies. Now I have been given the task to re-write an existing ERP application in C# (Winforms). I have been reading about Domain Driven Design, scrum, extreme programming, layered architecture etc. Its quite confusing and really hard (because of time limitations) to go and try each and every method and then deciding which way to go. Its very hard for me to understand the bigger picture and see which pattern and agile methodology to follow. To be more specific about what I want to know is that: Is it possible to follow Domain Driven Design and still be agile. Should I choose Extreme programming or scrum in this specific scenario Where does MVP and MVVM fits, which one would be a better option for me

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  • Singleton pattern and broken double checked locking in real world java application

    - by saugata
    I was reading the article Double-checked locking and the Singleton pattern, on how double checked locking is broken, and some related questions here on stackoverflow. I have used this pattern/idiom several times without any issues. Since I have been using Java 5, my first thought was that this has been rectified in Java 5 memory model. However the article says This article refers to the Java Memory Model before it was revised for Java 5.0; statements about memory ordering may no longer be correct. However, the double-checked locking idiom is still broken under the new memory model. I'm wondering if anyone has actually run into this problem in any application and under what conditions.

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  • Java Inter Application Form Communication Observer Pattern

    - by ikurtz
    Observer pattern? Where do i get examples of this in Java (i know google but was hoping for some personal insight also.) On to a proper explanation of my issue: i have 3 forms/windows. "board" is the main form that loads as the application. "chat" is where the text chat takes place. "network" is where network connection is established. i have the game (connect4) working locally and i would like to implement a networked version of it also. my idea is maybe it is related to Observer pattern to have a thread (or something) monitoring network state during runtime and update the chat and board forms of the current network status as well as delivering received data from the network. are my ideas valid? or how should i go about establishing network and network status updates throughout the application? thank you for your input.

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  • Idiom vs. pattern

    - by Roger Pate
    In the context of programming, how do idioms differ from patterns? I use the terms interchangeably and normally follow the most popular way I've heard something called, or the way it was called most recently in the current conversation, e.g. "the copy-swap idiom" and "singleton pattern". The best difference I can come up with is code which is meant to be copied almost literally is more often called pattern while code meant to be taken less literally is more often called idiom, but such isn't even always true. This doesn't seem to be more than a stylistic or buzzword difference. Does that match your perception of how the terms are used? Is there a semantic difference?

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  • EF and design pattern

    - by kathy
    Hello, I’m working on a high volume transactional enterprise application(asp.net, windows app, oracle app as client) which has been designed using n-tire application and SOA architecture .The application was developed in the .NET platform utilizing C#,VB.NET, Framework 3.5 (I’m planning to upgrade to the , Framework 4.0), EF( EF in the data layer level) and WCF(WCF services in the service layer level) Since this is the first project using EF, and having read about using EF in n-tier and SOA applications, and the features available in the EF Feature, I have the following points: Which design pattern should I use in EF( Simple Entities, Change Set, Self-Tracking Entities and DTOs) in the data layer level In addition Which design pattern should I use in the other tier and layer to get the best practices of EF Thanks

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  • split a string based on pattern in java - capital letters and numbers

    - by rookie
    Hi all I have the following string "3/4Ton". I want to split it as -- word[1] = 3/4 and word[2] = Ton. Right now my piece of code looks like this:- Pattern p = Pattern.compile("[A-Z]{1}[a-z]+"); Matcher m = p.matcher(line); while(m.find()){ System.out.println("The word --> "+m.group()); } It carries out the needed task of splitting the string based on capital letters like:- String = MachineryInput word[1] = Machinery , word[2] = Input The only problem is it does not preserve, numbers or abbreviations or sequences of capital letters which are not meant to be separate words. Could some one help me out with my regular expression coding problem. Thanks in advance...

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  • Database Replication OOD Pattern

    - by MrOnigiri
    Greetings fellow overflowers, After reading on MSDN about correct strategies on how to perform database replication, and understanding their suggestion on Master-Subordinate Incremental Replication. It left me wondering, what OOD design pattern should I use on this... The main elements of this strategy are the Acquirer, the Manipulator and the Writer. The first fetches data from the database and passes on to the second which might perform simple transformations to the data, before handling it to the final element, the writer, that writes the desired data on the destination Database. I thought about using the Chain of Responsibility pattern, but the Acquirer, Manipulator and Writer don't share a common role among theme, so It makes no sense. Should these elements be written as separate classes, or methods inside my service? Of course I'll be creating a DB Helper class as well, but that doesn't constitutes a problem. Wondering what your opinions on this are! Thanks for your replies

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