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  • C++ Singleton design pattern

    - by Artem Barger
    Recently I've bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real life example): // a lot of methods are omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that the instance field is initiated on the heap. That means there is a memory allocation. What is completely unclear for me is when exactly the memory is going to be deallocated? Or is there a bug and memory leak? It seems like there is a problem in the implementation. My main question is, how do I implement it in the right way?

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  • What exactly is GRASP's Controller about?

    - by devoured elysium
    What is the idea behind Grasp's Controller pattern? My current interpretation is that sometimes you want to achieve something that needs to use a couple of classes but none of those classes could or has access to the information needed to do it, so you create a new class that does the job, having references to all the needed classes(this is, could be the information expert). Is this a correct view of what Grasp's Controller is about? Generally when googling or SO'ing controller, I just get results about MVC's (and whatnot) which are topics that I don't understand about, so I'd like answers that don't assume I know ASP.NET's MVC or something :( Thanks

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  • group by country with ActiveRecords in Rails

    - by Adnan
    Hello, I have a table with users: name | country | .. | UK | .. | US | .. | US | .. | UK | .. | FR | .. | FR | .. | UK | .. | UK | .. | DE | .. | DE | .. | UK | .. | CA | . . What is the most efficient way with ActiveRecords to get the list of countries in my view and for each country how many users are from, so: US 123 UK 54 DE 33 . . .

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  • Tracking user changes in ASP.NET MVC

    - by Ian Roke
    I have a requirement to track what authenticated users change with regards to the data when logged in. I don't need to track what pages they look at although that could be very useful in future. I have thought about saving the User Guid but that seems very clunky. Are there other methods/best practises?

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  • Assignment in conditional operator

    - by DuoSRX
    I've seen a lot this kind of code recently : if ($foo = $bar->getFoo()) { baz($foo); } Is this considered good or bad practice ? For example, Netbeans IDE give a notice if you use this kind of code : Possible accidental assignment, assignments in conditions should be avoided What do you think ?

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  • Call a non member funcion on an instance before is constructed.

    - by Tom
    Hi everyone. I'm writing a class, and this doubt came up. Is this undef. behaviour? On the other hand, I'm not sure its recommended, or if its a good practice. Is it one if I ensure no exceptions to be thrown in the init function? //c.h class C{ float vx,vy; friend void init(C& c); public: C(); ~C(); }; //c.cpp C::C() { init(*this); } void init(C& c) //throws() to ensure no exceptions ? { c.vx = 0; c.vy = 0; } Thanks in advance

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  • Many-to-many relationship in oop

    - by Manu
    what is best way to model many-to-many relationship? lets say we have a two classes , Team and Player any given Player can be in multiple Team s any Team can have as many Player s as they like I like to call methods like playerX.getTeamList() to get the list of all the Team s he/she is in teamY.getPlayerList() to get the list of all the Player s in the team (or have some other way to do this effectively) I can think of two ways of doing this , but they just don't feels like good oop pattens. can you think of any good ways , perhaps a design patten ?

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  • What is the definition of a Service object ?

    - by Maskime
    I've been working a lot with PHP. But recently i was sent on a work wich use Java. In PHP i used to do a lot of Singleton object but this pattern has not the same signification in Java that it has in PHP. So i wanted to go for an utility class (a class with static method) but my chief doesn't like this kind of classes and ask me to go for services object. So my guess was that a service object is just a class with a constructor that implement some public methods... Am i right ?

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  • Makefile: expand dependencies

    - by Danyel
    First off, the title is very generic because there are just tons of ways of how to possibly solve this. However, I'm looking for a clean and neat way. Situation: I have two equal object files foo.o and foo-pi.o, the latter of which is position-independent (compiled with -fPIC). Both depend on foo.h and bar.h. Problem: How do I, without code duplication, declare dependency of all foo*.o to bar.h? Solutions so far: $(shell bash -c 'echo -ne foo{-pi,}.o'}: bar.h $(addsuffix .o, $(addprefix fo, o-pi o)): bar.h The first solution is not portable on systems that don't support bash, the second is a dirty solution since I could not figure out how to use empty strings in addprefix.

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  • new Integer vs valueOf

    - by LB
    Hi, I was using Sonar to make my code cleaner, and it pointed that I'm using new Integer(1) instead of Integer.valueOf(1). Because it seems that valueOf does not instantiate a new object so is more memory-friendly. How can valueOf not instantiate a new object ? How does it work ? Is this true for all integers ? thanks.

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  • UI Design - design pattern for city/country drop down? (ASP.NET MVC)

    - by JK
    What is the best way to do a city/country dropdown pair in ASP.NET MVC? I see lots of places with country above city, but that's unnatural: in real life we write city/country. I've used city, then country, but the problem is that the user then has to go backwards after changing the country. The other problem is what do you do about cities/countries not in your list? If city/country are both drop downs, then the user cant type their own city if it is missing. But if you have a dropdown and a textbox, that makes it unwieldy (you end up with 4 controls to enter 2 pieces of data). Are there any examples websites where the city/country dropdown pair are done in a very useable and clear manner?

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  • When using Sessions is bad thing, and whats wrong with it?

    - by Amr ElGarhy
    I know that in community server which means that you can't use Sessions, and few years ago i remember i was working on a website where we were not allowed to use sessions. In my point of view sessions are a very helpful tool if we managed how to use the right way, but is using session variable in a website is something bad, when its bad and when its not?

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  • Correct approach to validate attributes of an instance of class

    - by systempuntoout
    Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters declaration ? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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  • STLifying C++ classes

    - by shambulator
    I'm trying to write a class which contains several std::vectors as data members, and provides a subset of vector's interface to access them: class Mesh { public: private: std::vector<Vector3> positions; std::vector<Vector3> normals; // Several other members along the same lines }; The main thing you can do with a mesh is add positions, normals and other stuff to it. In order to allow an STL-like way of accessing a Mesh (add from arrays, other containers, etc.), I'm toying with the idea of adding methods like this: public: template<class InIter> void AddNormals(InIter first, InIter last); Problem is, from what I understand of templates, these methods will have to be defined in the header file (seems to make sense; without a concrete iterator type, the compiler doesn't know how to generate object code for the obvious implementation of this method). Is this actually a problem? My gut reaction is not to go around sticking huge chunks of code in header files, but my C++ is a little rusty with not much STL experience outside toy examples, and I'm not sure what "acceptable" C++ coding practice is on this. Is there a better way to expose this functionality while retaining an STL-like generic programming flavour? One way would be something like this: (end list) class RestrictedVector<T> { public: RestrictedVector(std::vector<T> wrapped) : wrapped(wrapped) {} template <class InIter> void Add(InIter first, InIter last) { std::copy(first, last, std::back_insert_iterator(wrapped)); } private: std::vector<T> wrapped; }; and then expose instances of these on Mesh instead, but that's starting to reek a little of overengineering :P Any advice is greatly appreciated!

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  • Implement abstract class as a local class? pros and cons

    - by sinec
    Hi, for some reason I'm thinking on implementing interface within a some function(method) as local class. Consider following: class A{ public: virtual void MethodToOverride() = 0; }; A * GetPtrToAImplementation(){ class B : public A { public: B(){} ~B(){} void MethodToOverride() { //do something } }; return static_cast<A *>(new B()); } int _tmain(int argc, _TCHAR* argv[]) { A * aInst = GetPtrToAImplementation(); aInst->MethodToOverride(); delete aInst; return 0; } the reason why I'm doing this are: I'm lazy to implement class (B) in separate files MethodToOverride just delegates call to other class Class B shouldn't be visible to other users no need to worry about deleting aInst since smart pointers are used in real implementation So my question is if I'm doing this right? Thanks in advance!

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  • How to change the value of progressbar in C#?

    - by shekhar
    Hi, I want to add an progress bar into my C# based application. I would like to know what is the good way of updating its value at particular events? My problem is, I have single function in UI which does all the processing.This function in turn calls many more functions, creates objects, updates database, etc. (basically performs all the work) and returns values in an output file. I have access to that function only. So in this how to update the progressbar's value at the end of each step? What is the best practice for this kind of situation? What is the good way to keep UI logic and business logic seperate? I want to avoid writting progressbar related code in my library code. Please suggest some solution. Thanks and Regards,

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  • Is it bad practice to initialize a variable to a dummy value?

    - by froadie
    This question is a result of the answers to this question that I just asked. It was claimed that this code is "ugly" because it initializes a variable to a value that will never be read: String tempName = null; try{ tempName = buildFileName(); } catch(Exception e){ ... System.exit(1); } FILE_NAME = tempName; Is this indeed bad practice? Should one avoid initializing variables to dummy values that will never actually be used? (EDIT - And what about initializing a String variable to "" before a loop that will concatenate values to the String...? Or is this in a separate category? e.g. String whatever = ""; for(String str : someCollection){ whatever += str; } )

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  • Should I use a class in this: Reading a XML file using lxml.

    - by PulpFiction
    Hi everyone. This question is in continuation to my previous question, in which I asked about passing around an ElementTree. I need to read the XML files only and to solve this, I decided to create a global ElementTree and then parse it wherever required. My question is: Is this an acceptable practice? I heard global variables are bad. If I don't make it global, I was suggested to make a class. But do I really need to create a class? What benefits would I have from that approach. Note that I would be handling only one ElementTree instance per run, the operations are read-only. If I don't use a class, how and where do I declare that ElementTree so that it available globally? (Note that I would be importing this module) Please answer this question in the respect that I am a beginner to development, and at this stage I can't figure out whether to use a class or just go with the functional style programming approach.

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  • Am i using too much jquery? When i'm crossing the line?

    - by Andrea
    Lately i find myself using jquery and javascript a lot, often to do the same things that i did before using css. For example, i alternate table rows color or create buttons and links hover effects using javascript/jquery. Is this acceptable? Or should i keep using css for these kind of things? So the real question is: When i'm using too much jquery? How can i understand when i'm crossing the line? Thanks.

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  • Call a non member function on an instance before is constructed.

    - by Tom
    Hi everyone. I'm writing a class, and this doubt came up. Is this undef. behaviour? On the other hand, I'm not sure its recommended, or if its a good practice. Is it one if I ensure no exceptions to be thrown in the init function? //c.h class C{ float vx,vy; friend void init(C& c); public: C(); }; //c.cpp C::C() { init(*this); } void init(C& c) //throws() to ensure no exceptions ? { c.vx = 0; c.vy = 0; } Thanks in advance

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  • correct technical term for this pattern

    - by Oliver A.
    sometimes I use a pattern which is very similar to the singleton pattern: There is one default instance which and a static get method to aces it. But you may create other instances and pass it as optional parameter and if you want to and you can even replace the default instance with a instance from a child class. So it is NO SINGLETON at all but it is used like one singleton in most cases. Anyone got an idea who to call something like this ? Maybe half*** singleton? domiton?

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  • UI to allow 700+ multiple choices

    - by Refracted Paladin
    In my desktop .NET application I have written(for internal use) where I need to allow my users to apply diagnosis's to a Member Plan. There are currently 700 in the system and growing. I need to allow them to add multiple diapnosis's at once. I currently am allowing this through a combo check list box. This works but is INSANELY unweildly for both myself and the users. What I am looking for is a how I could go about displaying these to the users. Ideally I would need to show two criteria for each each as well. Diagnosis Name and Diagnosis Code Ideas? How would you tackle this? I am using .Net 3.5sp1 and SQL 2005 for the backend. I don't care if the solution is WPF or Winforms.

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