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  • Composite pattern in C++ problem

    - by annouk
    Hello! I have to work with an application in C++ similar to a phone book: the class Agenda with an STL list of Contacts.Regarding the contacts hierarchy,there is a base-class named Contact(an abstract one),and the derived classes Friend and Acquaintance(the types of contact). These classes have,for instance, a virtual method called getName,which returns the name of the contact. Now I must implement the Composite pattern by adding another type of contact,Company(being derived from Contact),which also contains a collection of Contacts(an STL list as well),that can be either of the "leaf" type(Friends or Acquaintances),or they can be Companies as well. Therefore,Company is the Compound type. The question is: how and where can I implement an STL find_if to search the contact with a given name(via getName function or suggest me smth else) both among the "leaf"-type Contact and inside the Company collection? In other words,how do I traverse the tree in order to find possible matches there too,using an uniform function definition? I hope I was pretty clear...

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  • Exception handling pattern

    - by treefrog
    It is a common pattern I see where the error codes associated with an exception are stored as Static final ints. when the exception is created to be thrown, it is constructed with one of these codes along with an error message. This results in the method that is going to catch it having to look at the code and then decide on a course of action. The alternative seems to be- declare a class for EVERY exception error case Is there a middle ground ? what is the recommended method ?

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  • Pattern matching against Scala Map type

    - by Tom Morris
    Imagine I have a Map[String, String] in Scala. I want to match against the full set of key–value pairings in the map. Something like this ought to be possible val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace") record match { case Map("amenity" -> "restaurant", "cuisine" -> "chinese") => "a Chinese restaurant" case Map("amenity" -> "restaurant", "cuisine" -> "italian") => "an Italian restaurant" case Map("amenity" -> "restaurant") => "some other restaurant" case _ => "something else entirely" } The compiler complains thulsy: error: value Map is not a case class constructor, nor does it have an unapply/unapplySeq method What currently is the best way to pattern match for key–value combinations in a Map?

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  • Java Matcher groups: Understanding The difference between "(?:X|Y)" and "(?:X)|(?:Y)"

    - by user358795
    Can anyone explain: Why the two patterns used below give different results? (answered below) Why the 2nd example gives a group count of 1 but says the start and end of group 1 is -1? public void testGroups() throws Exception { String TEST_STRING = "After Yes is group 1 End"; { Pattern p; Matcher m; String pattern="(?:Yes|No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } { Pattern p; Matcher m; String pattern="(?:Yes)|(?:No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } } Which gives the following output: Pattern=(?:Yes|No)(.*)End Found=true Group count=1 Start of group 1=9 End of group 1=21 Pattern=(?:Yes)|(?:No)(.*)End Found=true Group count=1 Start of group 1=-1 End of group 1=-1

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  • MVC pattern and (Game) State pattern

    - by topright
    Game States separate I/O processing, game logic and rendering into different classes: while (game_loop) { game->state->io_events(this); game->state->logic(this); game->state->rendering(); } You can easily change a game state in this approach. MVC separation works in more complex way: while (game_loop) { game->cotroller->io_events(this); game->model->logic(this); game->view->rendering(); } So changing Game States becomes error prone task (switch 3 classes, not 1). What are practical ways of combining these 2 concepts?

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  • Adding line with text between pattern and next occurence of the same pattern in bash

    - by kasper
    I am writing a bash script that modifies a file that looks like this: --- usr1 --- data data data data data data data data data data data data --- usr2 --- data data data data data data data data --- usr3 --- data data data data --- endline --- One question is: How to add next user line --- usrn --- after last user data lines? Second one is: How to delete specific user data lines (data lines and --- userx ---) i.e. I would like to delete usr2 with all his data set. It must work on bash 2.05 :) and I think it will use awk or sed, but I'm not sure.

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  • Specification Pattern and Boolean Operator Precedence

    - by Anders Nielsen
    In our project, we have implemented the Specification Pattern with boolean operators (see DDD p 274), like so: public abstract class Rule { public Rule and(Rule rule) { return new AndRule(this, rule); } public Rule or(Rule rule) { return new OrRule(this, rule); } public Rule not() { return new NotRule(this); } public abstract boolean isSatisfied(T obj); } class AndRule extends Rule { private Rule one; private Rule two; AndRule(Rule one, Rule two) { this.one = one; this.two = two; } public boolean isSatisfied(T obj) { return one.isSatisfied(obj) && two.isSatisfied(obj); } } class OrRule extends Rule { private Rule one; private Rule two; OrRule(Rule one, Rule two) { this.one = one; this.two = two; } public boolean isSatisfied(T obj) { return one.isSatisfied(obj) || two.isSatisfied(obj); } } class NotRule extends Rule { private Rule rule; NotRule(Rule obj) { this.rule = obj; } public boolean isSatisfied(T obj) { return !rule.isSatisfied(obj); } } Which permits a nice expressiveness of the rules using method-chaining, but it doesn't support the standard operator precedence rules of which can lead to subtle errors. The following rules are not equivalent: Rule<Car> isNiceCar = isRed.and(isConvertible).or(isFerrari); Rule<Car> isNiceCar2 = isFerrari.or(isRed).and(isConvertible); The rule isNiceCar2 is not satisfied if the car is not a convertible, which can be confusing since if they were booleans isRed && isConvertible || isFerrari would be equivalent to isFerrari || isRed && isConvertible I realize that they would be equivalent if we rewrote isNiceCar2 to be isFerrari.or(isRed.and(isConvertible)), but both are syntactically correct. The best solution we can come up with, is to outlaw the method-chaining, and use constructors instead: OR(isFerrari, AND(isConvertible, isRed)) Does anyone have a better suggestion?

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  • Saving complex aggregates using Repository Pattern

    - by Kevin Lawrence
    We have a complex aggregate (sensitive names obfuscated for confidentiality reasons). The root, R, is composed of collections of Ms, As, Cs, Ss. Ms have collections of other low-level details. etc etc R really is an aggregate (no fair suggesting we split it!) We use lazy loading to retrieve the details. No problem there. But we are struggling a little with how to save such a complex aggregate. From the caller's point of view: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r); Our competing solutions are: Dirty flags Each entity in the aggregate in the aggregate has a dirty flag. The save() method in the repository walks the tree looking for dirty objects and saves them. Deletes and adds are a little trickier - especially with lazy-loading - but doable. Event listener accumulates changes. Repository subscribes a listener to changes and accumulates events. When save is called, the repository grabs all the change events and writes them to the DB. Give up on repository pattern. Implement overloaded save methods to save the parts of the aggregate separately. The original example would become: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r.Ps); repository.save(r.Cs); repository.save(r.Ms); (or worse) Advice please! What should we do?

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  • nhibernate fluent repository pattern insert problem

    - by voam
    I am trying to use Fluent NHibernate and the repository pattern. I would like my business layer to not be knowledgeable of the data persistence layer. Ideally I would pass in an initialized domain object to the insert method of the repository and all would be well. Where I run into problems is if the object being passed in has a child object. For example say I want to insert an a new order for a customer, and the customer is a property of the order object. I would like to do something like this: Customer c = new Customer; c.CustomerId = 1; Order o = new Order; o.Customer = c; repository.InsertOrder(o); The problem is that using NHiberate the CustomerId field is only privately settable so I can not set it directly like this. so what I have ended up doing is have my repository have an interface of Order InsertOrder(int customerId) where all the foreign keys get passed in as parameters. Somehow this just doesn't seem right. The other approach was to use the NHibernate session variable to load a customer object in my business model and then have the order passed in to the repository but this defeats my persistence ignorance ideal. Should I throw this persistence ignorance out the window or am I missing something here? Thanks

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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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  • Observer Design Pattern - multiple event types

    - by David
    I'm currently implementing the Observer design pattern and using it to handle adding items to the session, create error logs and write messages out to the user giving feedback on their actions (e.g. You've just logged out!). I began with a single method on the subject called addEvent() but as I added more Observers I found that the parameters required to detail all the information I needed for each listener began to grow. I now have 3 methods called addMessage(), addStorage() and addLog(). These add data into an events array that has a key related to the event type (e.g. log, message, storage) but I'm starting to feel that now the subject needs to know too much about the listeners that are attached. My alternative thought is to go back to addEvent() and pass an event type (e.g. USER_LOGOUT) along with the data associated and each Observer maintains it's own list of event handles it is looking for (possibly in a switch statement), but this feels cumbersome. Also, I'd need to check that sufficient data had also been passed along with the event type. What is the correct way of doing this? Please let me know if I can explain any parts of this further. I hope you can help and see the problem I'm battling with.

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  • Accessing jQuery objects in the module pattern

    - by Stewart
    Hello, Really getting in to javascript and looking around at some patterns. One I have come accross is the module pattern. Its seems like a nice way to think of chucks of functionality so I went ahead and tried to implement it with jQuery. I ran in to a snag though. Consider the following code <!DOCTYPE html> <html> <head> <meta http-equiv="Content-type" content="text/html; charset=utf-8"> <title>index</title> <script type="text/javascript" charset="utf-8" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script> <script type="text/javascript" charset="utf-8"> $(document).ready(function(){ var TestClass2 = (function(){ var someDiv; return { thisTest: function () { someDiv = document.createElement("div"); $(someDiv).append("#index"); $(someDiv).html("hello"); $(someDiv).addClass("test_class"); } } })(); TestClass2.thisTest(); }); </script> </head> <body id="index" onload=""> <div id="name"> this is content </div> </body> </html> The above code alerts the html content of the div and then adds a class. These both use jQuery methods. The problem is that the .html() method works fine however i can not add the class. No errors result and the class does not get added. What is happening here? Why is the class not getting added to the div?

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  • f# pattern matching with types

    - by philbrowndotcom
    I'm trying to recursively print out all an objects properties and sub-type properties etc. My object model is as follows... type suggestedFooWidget = { value: float ; hasIncreasedSinceLastPeriod: bool ; } type firmIdentifier = { firmId: int ; firmName: string ; } type authorIdentifier = { authorId: int ; authorName: string ; firm: firmIdentifier ; } type denormalizedSuggestedFooWidgets = { id: int ; ticker: string ; direction: string ; author: authorIdentifier ; totalAbsoluteWidget: suggestedFooWidget ; totalSectorWidget: suggestedFooWidget ; totalExchangeWidget: suggestedFooWidget ; todaysAbsoluteWidget: suggestedFooWidget ; msdAbsoluteWidget: suggestedFooWidget ; msdSectorWidget: suggestedFooWidget ; msdExchangeWidget: suggestedFooWidget ; } And my recursion is based on the following pattern matching... let rec printObj (o : obj) (sb : StringBuilder) (depth : int) let props = o.GetType().GetProperties() let enumer = props.GetEnumerator() while enumer.MoveNext() do let currObj = (enumer.Current : obj) ignore <| match currObj with | :? string as s -> sb.Append(s.ToString()) | :? bool as c -> sb.Append(c.ToString()) | :? int as i -> sb.Append(i.ToString()) | :? float as i -> sb.Append(i.ToString()) | _ -> printObj currObj sb (depth + 1) sb In the debugger I see that currObj is of type string, int, float, etc but it always jumps to the defualt case at the bottom. Any idea why this is happening?

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  • Modified Strategy Design Pattern

    - by Samuel Walker
    I've started looking into Design Patterns recently, and one thing I'm coding would suit the Strategy pattern perfectly, except for one small difference. Essentially, some (but not all) of my algorithms, need an extra parameter or two passed to them. So I'll either need to pass them an extra parameter when I invoke their calculate method or store them as variables inside the ConcreteAlgorithm class, and be able to update them before I call the algorithm. Is there a design pattern for this need / How could I implement this while sticking to the Strategy Pattern? I've considered passing the client object to all the algorithms, and storing the variables in there, then using that only when the particular algorithm needs it. However, I think this is both unwieldy, and defeats the point of the strategy pattern. Just to be clear I'm implementing in Java, and so don't have the luxury of optional parameters (which would solve this nicely).

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  • Design Pattern Advice for Bluetooth App for Android

    - by Aimee Jones
    I’m looking for some advice on which patterns would apply to some of my work. I’m planning on doing a project as part of my college work and I need a bit of help. My main project is to make a basic Android bluetooth tracking system where the fixed locations of bluetooth dongles are mapped onto a map of a building. So my android app will regularly scan for nearby dongles and triangulate its location based on signal strength. The dongles location would be saved to a database along with their mac addresses to differentiate between them. The android phones location will then be sent to a server. This information will be used to show the phone’s location on a map of the building, or map of a route taken, on a website. My side project is to choose a suitable design pattern that could be implemented in this main project. I’m still a bit new to design patterns and am finding it hard to get my head around ones that may be suitable. I’ve heard maybe some that are aimed at web applications for the server side of things may be appropriate. My research so far is leading me to the following: Navigation Strategy Pattern Observer Pattern Command Pattern News Design Pattern Any advice would be a great help! Thanks

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  • Incorporating libs into module pattern

    - by webnesto
    I have recently started using require.js (along with Backbone.js, jQuery, and a handful of other JavaScript libs) and I love the module pattern (here's a nice synopsis if you're unfamiliar: http://www.adequatelygood.com/2010/3/JavaScript-Module-Pattern-In-Depth). Something I'm running up against is best practices on incorporating libs that don't (out of the box) support the module pattern. For example, jQuery without modification is going to load into a global jQuery variable and that's that. Require.js recognizes this and provides an example project for download with a (slightly) modified version of jQuery to incorporate with a require.js project. This goes against everything I've ever learned about using external libs - never modify the source. I can list a ton of reasons. Regardless, this is not an approach I'm comfortable with. I have been using a mixed approach - wherein I build/load the "traditional" JS libraries in a "traditional" way (available in the global namespace) and then using the module pattern for all of my application code. This seems okay to me, but it bugs me because one of the real beauties of the module pattern (no globals) is getting perverted. Anyone else got a better solution to this problem?

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  • The repository pattern explained and implemented

    The pattern documented and named Repository is one of the most misunderstood and misused. In this post well implement the pattern in C# to achieve this simple line of code: var customers = customers.Matching(new PremiumCustomersFilter()) as well as discuss the origins of the pattern and the original definitions to clear out some of the misrepresentations. [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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