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  • Force an object to be allocated on the heap

    - by Warren Seine
    A C++ class I'm writing uses shared_from_this() to return a valid boost::shared_ptr<>. Besides, I don't want to manage memory for this kind of object. At the moment, I'm not restricting the way the user allocates the object, which causes an error if shared_from_this() is called on a stack-allocated object. I'd like to force the object to be allocated with new and managed by a smart pointer, no matter how the user declares it. I thought it could be done through a proxy or an overloaded new operator, but I can't find a proper way of doing that. Is there a common design pattern for such usage? If it's not possible, how can I test it at compile time?

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  • when to make a method static

    - by Don
    Hi, I'd like to know how people decide whether to define a method as static. I'm aware that a method can only be defined as static if it doesn't require access to instance fields. So lets say we have a method that does not access instance fields, do you always define such a method as static, or only if you need to call it statically (without a reference to an instance). Perhaps another way of asking the same question, is whether you use static or non-static as the default? Thanks, Don

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  • Should I put actors in the Domain-Model/Class-Diagram?

    - by devoured elysium
    When designing both the domain-model and class-diagrams I am having some trouble understanding what to put in them. I'll give an example of what I mean: I am doing a vacations scheduler program, that has an Administrator and End-Users. The Administrator does a couple of things like registering End-Users in the program, changing their previleges, etc. The End-User can choose his vacations days, etc. I initially defined an Administrator and End-User as concepts in the domain-model, and later as classes in the class-diagram. In the class-diagram, both classes ended up having a couple of methods like Administrator.RegisterNewUser(); Administrator.UnregisterUser(int id); etc. Only after some time I realised that actually both Administrator and End-User are actors, and maybe I got this design totally wrong. Instead of filling Administrator and End-User classes with methods to do what my Use-Cases request, I could define other classes from the domain to do them, and have controllers handle the Use-Cases(actually, I decided to do one for each Use-Case). I could have a UserDatabase.RegisterNewUser() and UserDatabase.UnregisterUser(int id);, for example, instead of having those methods on the Administrator class. The idea would be to try to think of the whole vacation-scheduler as a "closed-program" that has a set of features and doesn't bother with things such as authentication, that should be internal/protected, being that the only public things I'd let the outside world see would be its controllers. Is this the right approach? Or am I getting this totally wrong? Is it generally bad idea to put Actors in the domain-model/class-diagrams? What are good rules of thumb for this? My lecturer is following Applying UML and Patterns, which I find awful, so I'd like to know where I could look up more info on this described actor-models situation. I'm still a bit confused about all of this, as this new approach is radically different from anything I've done before.

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  • When to define SDD(System Sequence Diagram) operations System->Actor?

    - by devoured elysium
    I am having some trouble understanding how to make System Sequence Diagrams, as I don't fully grasp why in some cases one should define operations for System - Actor and in others don't. Here is an example: Let's assume the System is a Cinema Ticket Store and the Actor is a client that wants to buy a ticket. 1) The User tells the System that wants to buy some tickets, stating his client number. 2) The System confirms that the given client number is valid. 3) The User tells the System the movie that wants to see. 4) The System shows the set of available sessions and seats for that movie. 5) The System asks the user which session/seat he wants. 6) The User tells the System the chosen session/seat. This would be converted to: a) -----> tellClientNumber(clientNumber) b) <----- validClientNumber c) -----> tellMovieToSee(movie) d) <----- showsAvailableSeatsHours e) -----> tellSystemChosenSessionSeat(session, seat) I know that when we are dealing with SDD's we are still far away from coding. But I can't help trying to imagine how it how it would have been had I to convert it right away to code: I can understand 1) and 2). It's like if it was a C#/Java method with the following signature: boolean tellClientNumber(clientNumber) so I put both on the SDD. Then, we have the pair 3) 4). I can imagine that as something as: SomeDataStructureThatHoldsAvailableSessionsSeats tellSystemMovieToSee(movie) Now, the problem: From what I've come to understand, my lecturer says that we shouldn't make an operation on the SDD for 5) as we should only show operations from the Actor to the System and when the System is either presenting us data (as in c)) or validating sent data (such as in b)). I find this odd, as if I try to imagine this like a DOS app where you have to put your input sequencially, it makes sense to make an arrow even for 5). Why is this wrong? How should I try to visualize this? Thanks

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  • Is it possible to change the file path of the video using javascript?

    - by Manish
    I have an object tag in a HTML file: <object classid="clsid:22D6F312-B0F6-11D0-94AB-0080C74C7E95"> <param name="FileName" value="../ABC/WildLife.wmv" id="mediaPlayerFile"> <param name="AutoStart" value="false" /> </object> I want to change the filename using javascript. What I have so far is this: <script type="text/javascript"> function disp_current_directory() { var val = document.getElementById('mediaPlayerFile'); val.attributes['value'].value = "D:\XYZ\WildLife.wmv"; } </script> But this doesn't work. :( Is it possible? If yes, how?

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  • PHP Store User Data without Sessions

    - by Sev
    Is there anyway to store users data such as userid, email, etc to be accessible from all pages of a website after they have logged in, but without using sessions or cookies? For example: class User { var $userid; var $username; var $email; .. methods.. } after they login at login.php $currentUser = new User($_POST['username']) now, how do I access $currentUser from another page, such as index.php if I shouldn't use sessions or cookies at all? so that I could do the following in index.php: if ($currentUser->userid > -1) { echo "you are logged in as: " . $currentUser->username; } else { echo "click here to login"; } i asked a similar question before, here, but the answers didn't fulfill my needs.

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  • multiple models in Rails with a shared interface

    - by dfondente
    I'm not sure of the best structure for a particular situation in Rails. We have several types of workshops. The administration of the workshops is the same regardless of workshop type, so the data for the workshops is in a single model. We collect feedback from participants about the workshops, and the questionnaire is different for each type of workshop. I want to access the feedback about the workshop from the workshop model, but the class of the associated model will depend on the type of workshop. If I was doing this in something other than Rails, I would set up an abstract class for WorkshopFeedback, and then have subclasses for each type of workshop: WorkshopFeedbackOne, WorkshopFeedbackTwo, WorkshopFeedbackThree. I'm unsure how to best handle this with Rails. I currently have: class Workshop < ActiveRecord::Base has_many :workshop_feedbacks end class Feedback < ActiveRecord::Base belongs_to :workshop has_many :feedback_ones has_many :feedback_twos has_many :feedback_threes end class FeedbackOne < ActiveRecord::Base belongs_to :feedback end class FeedbackTwo < ActiveRecord::Base belongs_to :feedback end class FeedbackThree < ActiveRecord::Base belongs_to :feedback end This doesn't seem like to the cleanest way to access the feedback from the workshop model, as accessing the correct feedback will require logic investigating the Workshop type and then choosing, for instance, @workshop.feedback.feedback_one. Is there a better way to handle this situation? Would it be better to use a polymorphic association for feedback? Or maybe using a Module or Mixin for the shared Feedback interface? Note: I am avoiding using Single Table Inheritance here because the FeedbackOne, FeedbackTwo, FeedbackThree models do not share much common data, so I would end up with a large sparsely populated table with STI.

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  • Passing arguments between classes - use public properties or pass a properties class as argument?

    - by devoured elysium
    So let's assume I have a class named ABC that will have a list of Point objects. I need to make some drawing logic with them. Each one of those Point objects will have a Draw() method that will be called by the ABC class. The Draw() method code will need info from ABC class. I can only see two ways to make them have this info: Having Abc class make public some properties that would allow draw() to make its decisions. Having Abc class pass to draw() a class full of properties. The properties in both cases would be the same, my question is what is preferred in this case. Maybe the second approach is more flexible? Maybe not? I don't see here a clear winner, but that sure has more to do with my inexperience than any other thing. If there are other good approaches, feel free to share them. Here are both cases: class Abc1 { public property a; public property b; public property c; ... public property z; public void method1(); ... public void methodn(); } and here is approach 2: class Abc2 { //here we make take down all properties public void method1(); ... public void methodn(); } class Abc2MethodArgs { //and we put them here. this class will be passed as argument to //Point's draw() method! public property a; public property b; public property c; ... public property z; } Also, if there are any "formal" names for these two approaches, I'd like to know them so I can better choose the tags/thread name, so it's more useful for searching purposes. That or feel free to edit them.

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  • Best ways to construct Dynamic Search Conditions for Sql

    - by CoolBeans
    I have always wondered what's the best way to achieve this task. In most web based applications you have to provide search options on many different criteria. Based on what criteria is chosen behind the scene you modify your SQL. Generally, this is how I tend to go about it:- Have a base SQL template. In the base template have conditions like this WHERE [#PRE_COND1] AND [#PRE_COND2] .. so on and so forth. So an example SQL might look something like SELECT NAME,AGE FROM PERSONS [,#TABLE2] [,#TABLE3] WHERE [#PRE_COND1] AND [#PRE_COND2] ORDER BY [#ORD_COND1] AND [#ORD_COND2] etc. During run time after figuring out the all the search criteria user has entered, I replace the [#PRE_COND1]s and [#ORD_COND1]s with the appropriate SQLs and then execute the query. I personally do not like this brute force method. However, I never came across a better approach either. How do you accomplish such tasks generally given you are either using native JDBC or Spring JDBC? It is almost like I need a C MACRO like functionality in Java to do this.

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  • Class architecture, no friends allowed

    - by Captain Comic
    The question of why there are no friends in C# has been extensively discussed. I have the following design problems. I have a class that has only one public function AddOrder(Order ord). Clients are allowed to call only this function. All other logic must be hidden. Order class is listening to market events and must call other other function of TradingSystem ExecuteOrder, so I have to make it public as well. Doing that I will allow clients of Trading system to call this function and I don't want that. class TradingSystem { // Trading system stores list of orders List<Order> _orders; // this function is made public so that Order can call ir public ExecuteOrder(Order ord) { } // this function is made public for external clients public AddOrder(OrderRequest ordreq) { // create order and pass it this order.OnOrderAdded(this); } } class Order { TradingSystem _ts; public void OnOrderAdded(TradingSystem ts) { _ts = ts; } void OnMarketEvent() { _ts.ExecuteOrder() } }

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  • Persistance Queue Implementation

    - by Winter
    I was reading an article on Batch Processing in java over at JDJ http://java.sys-con.com/node/415321 . The article mentioned using a persistence queue as a Batch Updater instead of immediately sending an individual insert or update to the database. The author doesn't give a concrete example of this concept so I googled Persistence Queue but that didn't come up with much. Does anyone know of a good example of this?

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  • Why can't I create an abstract constructor on an abstract C# class?

    - by Anthony D
    I am creating an abstract class. I want each of my derived classes to be forced to implement a specific signature of constructor. As such, I did what I would have done has I wanted to force them to implement a method, I made an abstract one. public abstract class A { abstract A(int a, int b); } However I get a message saying the abstract modifier is invalid on this item. My goal was to force some code like this. public class B : A { public B(int a, int b) : base(a, b) { //Some other awesome code. } } This is all C# .NET code. Can anyone help me out? Update 1 I wanted to add some things. What I ended up with was this. private A() { } protected A(int a, int b) { //Code } That does what some folks are saying, default is private, and the class needs to implement a constructor. However that doesn't FORCE a constructor with the signature A(int a, int b). public abstract class A { protected abstract A(int a, int b) { } } Update 2 I should be clear, to work around this I made my default constructor private, and my other constructor protected. I am not really looking for a way to make my code work. I took care of that. I am looking to understand why C# does not let you do this.

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  • Design issue when having classes implement different interfaces to restrict client actions

    - by devoured elysium
    Let's say I'm defining a game class that implements two different views: interface IPlayerView { void play(); } interface IDealerView { void deal(); } The view that a game sees when playing the game, and a view that the dealer sees when dealing the game (this is, a player can't make dealer actions and a dealer can't make player actions). The game definition is as following: class Game : IPlayerView, IDealerView { void play() { ... } void deal() { ... } } Now assume I want to make it possible for the players to play the game, but not to deal it. My original idea was that instead of having public Game GetGame() { ... } I'd have something like public IPlayerView GetGame() { ... } But after some tests I realized that if I later try this code, it works: IDealerView dealerView = (IDealerView)GameClass.GetGame(); this works as lets the user act as the dealer. Am I worrying to much? How do you usually deal with this patterns? I could instead make two different classes, maybe a "main" class, the dealer class, that would act as factory of player classes. That way I could control exactly what I would like to pass on the the public. On the other hand, that turns everything a bit more complex than with this original design. Thanks

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  • grab inspect the parameters to "use" and pass on the rest?

    - by JoelFan
    I have a Perl module and I'd like to be able to pick out the parameters that my my module's user passed in the "use" call. Whichever ones I don't recognize I'd like to pass on. I tried to do this by overriding the "import" method but I'm not having much luck. EDIT: To clarify, as it is, I can use my module like this: use MyModule qw/foo bar/; which will import the foo and bar methods of MyModule. But I want to be able to say: use MyModule qw/foo doSpecialStuff bar/; and look for doSpecialStuff to check if I need to do some special stuff at the beginning of the program, then pass qw/foo bar/ to the Exporter's import

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  • What is the Rule of Thumb on Exposing Encapsulated Class Methods

    - by javamonkey79
    Consider the following analogy: If we have a class: "Car" we might expect it to have an instance of "Engine" in it. As in: "The car HAS-A engine". Similarly, in the "Engine" class we would expect an instance of "Starting System" or "Cooling System" which each have their appropriate sub-components. By the nature of encapsulation, is it not true that the car "HAS-A" "radiator hose" in it as well as the engine? Therefore, is it appropriate OO to do something like this: public class Car { private Engine _engine; public Engine getEngine() { return _engine; } // is it ok to use 'convenience' methods of inner classes? // are the following 2 methods "wrong" from an OO point of view? public RadiatorHose getRadiatorHose() { return getCoolingSystem().getRadiatorHose(); } public CoolingSystem getCoolingSystem() { return _engine.getCoolingSystem(); } } public class Engine { private CoolingSystem _coolingSystem; public CoolingSystem getCoolingSystem() { return _coolingSystem; } } public class CoolingSystem { private RadiatorHose _radiatorHose; public RadiatorHose getRadiatorHose() { return _radiatorHose; } } public class RadiatorHose {//... }

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  • Simple OOP-related question.

    - by M4design
    This question came to my mind quite a few times. Let my explain my question through an example. Say I've got two classes: 1- Grid. 2- Cell. Now the location of the cell 'should' be stored in the grid class, not in the cell class itself. Say that the cell wanted to get its location through a method in the grid. How can it do that? Keep in mind that the cell was created/initialised by the Grid class. What good OO approach to solve this problem? Thank you

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  • Rails - before_filter than includes updated object

    - by Sam
    I have a before filter than calculates a percentage that needs to include the object that is being updated. Is there a one liner in rails that takes care of this? for example and this is totaly made up: Object.find(:all, :include = :updated_object) Currently I'm sending the object that is getting updated to the definition that calculates the percentage and that works but its making things messy.

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  • How can I find out how much memory an instance of a C++ class consumes?

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • Adding property:value pairs from GooglemapsAPI to an existing json/javascript object

    - by Rockinelle
    I am trying to create a script that finds the closest store/location to a customer using googlemapsAPI. So I've got a json object which is a collection of store objects. Using Jquery's .each to iterate through that object, I am grabbing the driving time from the customer to each store. If it finds the directions, It copies the duration of the drive which is an object with the time in seconds and a human readable value. That appears to work, however when I try to sort through all of those store objects with the drivetime added, I cannot read the object copied from google. If I console.log the whole object, 'closest_store', It shows the values I'm looking for. When I try to read the values directly via closest_store.driveTime, Firebug is outputting undefined in the console. What am I missing here? $.getJSON('<?php echo Url::base() ?>oldservices/get_locations', {}, function(data){ $.each(data, function(index, value) { var end = data[index].address; var request = { origin: start, destination: end, travelMode: google.maps.DirectionsTravelMode.DRIVING }; directionsService.route(request, function(response, status) { //console.log(response); if (status == google.maps.DirectionsStatus.OK) { value.driveTime = response.trips[0].routes[0].duration.value; //console.log(response.trips[0].routes[0].duration.value); }; }); }); var closest_store; $.each(data, function(index, current_store) { if (index == 0) { closest_store = current_store; } else if (current_store.driveTime.value < closest_store.driveTime.value) { closest_store = value }; console.log(current_store.driveTime); } ) });

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  • How to call virtual function of an object in C++

    - by SoonDead
    I'm struggling with calling a virtual function in C++. I'm not experienced in C++, I mainly use C# and Java so I might have some delusions, but bear with me. I have to write a program where I have to avoid dynamic memory allocation if possible. I have made a class called List: template <class T> class List { public: T items[maxListLength]; int length; List() { length = 0; } T get(int i) const { if (i >= 0 && i < length) { return items[i]; } else { throw "Out of range!"; } }; // set the value of an already existing element void set(int i, T p) { if (i >= 0 && i < length) { items[i] = p; } else { throw "Out of range!"; } } // returns the index of the element int add(T p) { if (length >= maxListLength) { throw "Too many points!"; } items[length] = p; return length++; } // removes and returns the last element; T pop() { if (length > 0) { return items[--length]; } else { throw "There is no element to remove!"; } } }; It just makes an array of the given type, and manages the length of it. There is no need for dynamic memory allocation, I can just write: List<Object> objects; MyObject obj; objects.add(obj); MyObject inherits form Object. Object has a virtual function which is supposed to be overridden in MyObject: struct Object { virtual float method(const Input& input) { return 0.0f; } }; struct MyObject: public Object { virtual float method(const Input& input) { return 1.0f; } }; I get the elements as: objects.get(0).method(asdf); The problem is that even though the first element is a MyObject, the Object's method function is called. I'm guessing there is something wrong with storing the object in an array of Objects without dynamically allocating memory for the MyObject, but I'm not sure. Is there a way to call MyObject's method function? How? It's supposed to be a heterogeneous collection btw, so that's why the inheritance is there in the first place. If there is no way to call the MyObject's method function, then how should I make my list in the first place?

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  • Database model for storing expressions and their occurrence in text

    - by lisak
    Hey, I'm doing a statistical research application. I need to store words according to 2 initial letters which is 676 combinations and each word has its number of occurrences (minimal, maximal, average) in text. I'm not sure how the model/schema should look like. There will be a lot of checking whether the keyword was already persisted. I appreciate your suggestions. Edit: I'll be using either mysql or postgresql + spring templates

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