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  • C++ Return by reference

    - by Gokul
    Say, i have a function which returns a reference and i want to make sure that the caller only gets it as a reference and should not receive it as a copy. Is this possible in C++? Thanks, Gokul.

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  • Is there a difference between `==` and `is` in python?

    - by Bernard
    My Google-fu has failed me. In Python, are these: n = 5 # Test one. if n == 5: print 'Yay!' # Test two. if n is 5: print 'Yay!' two tests for equality equivalent (ha!)? Does this hold true for objects where you would be comparing instances (a list say)? Okay, so this kind of answers my question: l = list() l.append(1) if l == [1]: print 'Yay!' # Holds true, but... if l is [1]: print 'Yay!' # Doesn't. So == tests value where is tests to see if they are the same object?

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  • How can I declare classes that refer to each other?

    - by Without me Its just Aweso
    It's been a long time since I've done C++ and I'm running into some trouble with classes referencing each other. Right now I have something like: a.h class a { public: a(); bool skeletonfunc(b temp); }; b.h class b { public: b(); bool skeletonfunc(a temp); }; Since each one needs a reference to the other, I've found I can't do a #include of each other at the top or I end up in a weird loop of sorts with the includes. So how can I make it so that a can use b and vice versa without making a cyclical #include problem? thanks!

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  • Criteria for triggering garbage collection in .Net

    - by Kennet Belenky
    I've come across some curious behavior with regard to garbage collection in .Net. The following program will throw an OutOfMemoryException very quickly (after less than a second on a 32-bit, 2GB machine). The Foo finalizer is never called. class Foo { static Dictionary<Guid, WeakReference> allFoos = new Dictionary<Guid, WeakReference>(); Guid guid = Guid.NewGuid(); byte[] buffer = new byte[1000000]; static Random rand = new Random(); public Foo() { // Uncomment the following line and the program will run forever. // rand.NextBytes(buffer); allFoos[guid] = new WeakReference(this); } ~Foo() { allFoos.Remove(guid); } static public void Main(string args[]) { for (; ; ) { new Foo(); } } } If the rand.nextBytes line is uncommented, it will run ad infinitum, and the Foo finalizer is regularly invoked. Why is that? My best guess is that in the former case, either the CLR or the Windows VMM is lazy about allocating physical memory. The buffer never gets written to, so the physical memory is never used. When the address space runs out, the system crashes. In the latter case, the system runs out of physical memory before it runs out of address space, the GC is triggered and the objects are collected. However, here's the part I don't get. Assuming my theory is correct, why doesn't the GC trigger when the address space runs low? If my theory is incorrect, then what's the real explanation?

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  • Is it bad OOP practice to have objects reference each other?

    - by lala
    Pardon my noobness. I'm making a game in which several characters have relationships with each other and they need to be able to interact with each other and store some relationship data regarding how they feel about each other. I have an object for each character. Is it bad for each of those character objects to have an array of all the other character objects in order to perform these interactions? Is there a better way to do this?

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  • why no implicit conversion from pointer to reference to const pointer.

    - by user316606
    I'll illustrate my question with code: #include <iostream> void PrintInt(const unsigned char*& ptr) { int data = 0; ::memcpy(&data, ptr, sizeof(data)); // advance the pointer reference. ptr += sizeof(data); std::cout << std::hex << data << " " << std::endl; } int main(int, char**) { unsigned char buffer[] = { 0x11, 0x11, 0x11, 0x11, 0x22, 0x22, 0x22, 0x22, }; /* const */ unsigned char* ptr = buffer; PrintInt(ptr); // error C2664: ... PrintInt(ptr); // error C2664: ... return 0; } When I run this code (in VS2008) I get this: error C2664: 'PrintInt' : cannot convert parameter 1 from 'unsigned char *' to 'const unsigned char *&'. If I uncomment the "const" comment it works fine. However shouldn't pointer implicitly convert into const pointer and then reference be taken? Am I wrong in expecting this to work? Thanks!

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  • C++ const-reference semantics?

    - by Kristoffer
    Consider the sample application below. It demonstrates what I would call a flawed class design. #include <iostream> using namespace std; struct B { B() : m_value(1) {} long m_value; }; struct A { const B& GetB() const { return m_B; } void Foo(const B &b) { // assert(this != &b); m_B.m_value += b.m_value; m_B.m_value += b.m_value; } protected: B m_B; }; int main(int argc, char* argv[]) { A a; cout << "Original value: " << a.GetB().m_value << endl; cout << "Expected value: 3" << endl; a.Foo(a.GetB()); cout << "Actual value: " << a.GetB().m_value << endl; return 0; } Output: Original value: 1 Expected value: 3 Actual value: 4 Obviously, the programmer is fooled by the constness of b. By mistake b points to this, which yields the undesired behavior. My question: What const-rules should you follow when designing getters/setters? My suggestion: Never return a reference to a member variable if it can be set by reference through a member function. Hence, either return by value or pass parameters by value. (Modern compilers will optimize away the extra copy anyway.)

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  • Postion of & to denote reference type

    - by Matt H
    I was wondering whether to put the ampersand (&) after the variable type or before the variable name. To put it simply, I want to know which one is the conventional style or the standard, or if it is entirely down to preference. int &x; or int& x;

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  • Simple C++ classes question

    - by Without me Its just Aweso
    Its been a long time since i've done C++ and I'm running into some trouble with classes referencing eachother. right now I have something like: a.h class a { public: a(); bool skeletonfunc(b temp); } ==================== b.h class b { public: b(); bool skeletonfunc(a temp); } since each one needs a reference to the other i've found I cant do a #include of eachother at the top or i end up in a weird loop of sorts with the includes. So how can I make it so that a can use b and vice versa with out making a cyclical #include problem. thanks!

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  • Strategies for dealing with Circular references caused by JPA relationships?

    - by ams
    I am trying to partition my application into modules by features packaged into separate jars such as feature-a.jar, feature-b.jar, ... etc. Individual feature jars such as feature-a.jar should contain all the code for a feature a including jpa entities, business logic, rest apis, unit tests, integration test ... etc. The problem I am running into is that bi-directional relationships between JPA entities cause circular references between the jar files. For example Customer entity should be in customer.jar and the Order should be in order.jar but Customer references order and order references customer making it hard to split them into separate jars / eclipse projects. Options I see for dealing with the circular dependencies in JPA entities: Option 1: Put all the entities into one jar / one project Option 2: Don't map certain bi-directianl relationships to avoid circular dependencies across projects. Questions: What rules / principles have you used to decide when to do bi-directional mapping vs. not? Have you been able to break jpa entities into their own projects / jar by features if so how did you avoid the circular dependencies issues?

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  • Can an aggregate root hold references of members of another aggregate root?

    - by Rushino
    Hello, I know outside aggregates cant change anything inside an aggregate without passing by his root. That said i would like to know if an aggregate root can hold references of members (objects insides) of another aggregate root? (fellowing DDD rules) Example : a Calendar contain a list of phases which contain a list of sequences which contain a list of assignations Calendar is root because phases and sequences and assignations only work in context of a calendar. You also have Students and Groups of student (called groups) It is possible (fellowing DDD rules) to make Groups holding references of assignations or it need to pass by the root for accessing groups from assignations ? Thanks.

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  • Question between aggregations, compositions, references (arrow) and simple link (nothing) relations within UML2 ?

    - by Rushino
    Hello, I have some questions regarding relations between aggregations, compositions, references (arrow) and simple link (nothing) relations within UML2 ? If A - B - C each have composition relationship. Are the root responsable of creation and destruction of the object B and C ? What aggregations have that the simple link or references doesn't ? What make them different ? Thanks. Edit: The question was a bit unclear and not objective. I edited it.

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  • SOA &amp; Application Grid Specialization step 2 of 6 &ndash; References &amp; Marketing Kits

    - by Jürgen Kress
    In our fist step to become SOA Specialized & Application Grid Specialized we highlighted our OMM to register your opportunities. We continue our path to specialization with our marketing offerings to create your reference cases and run joint marketing campaigns. References: Be Recognized Through Partner Success Stories Oracle delivers a wide variety of services and solutions through our partners and we believe that those successes should be recognized and promoted. References are also required to become specialized. We showcase our partners’ capabilities in Oracle products and industries through partner success stories that are published on Oracle.com. For significant implementations, we may invite partners to participate in a press release or be interviewed in a podcast. To participate and take a further step to become specialized, please take a minute to complete the form and tell us about the successful project you have implemented. If your story is selected, we will contact you for an interview. Create your references The partner reference program Enables partners to be recognized by both Oracle and our customers Provides an opportunity for partners to showcase successes with their customers on Oracle solutions Helps raise awareness of our partners’ capabilities, elevating them above their competition Time to submit a SOA and Application Grid reference request today To learn more about partner references, check out the following resources: Judson Althoff’s YouTube Video: Be Recognized with OPN Specialized Reference Program OPN PartnerCast: Be Recognized…Your Reference Matters!!! (MP3) Partner/Customer Reference Brochure (PDF) Marketing Kits We have created OFM 11g marketing kit http://tinyurl.com/soamarketing (OPN account required) The marketing kit includes all the ppts and demos from our launch event. Oracle package includes: • Event templates like invitation, agenda ,confirmation follow up templates • OFM 11g presentations • Free usage of the Oracle Customer Visit Center • Condition: mandatory lead registration in the Oracle Open Market Model (OMM) To download the material, please make sure that you select the campaign “Enterprise: Fusion Middleware 11g”: OFM 11g Oracle Marketing 4 Partners Package http://tinyurl.com/soamarketing (OPN account required)   For more information on Specialization please visit our OPN Specialized Webcast Series And become a member in our SOA Partner Community for registration please visit www.oracle.com/goto/ema/soa Jürgen Kress, SOA Partner Adoption EMEA SOA Specialized Application Grid Specialized Proof 2 transactions with OMM Proof 2 transactions with OMM Create your 2 references Create your 2 references SOA Sales assessment 3, Oracle Application Grid Sales Specialist  SOA Pre-Sales assessment 3 Oracle Application Grid PreSales Specialist Support assessment 1 Support assessment 2 SOA Implementation assessment 4 Application Gridplementation assessment 4

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  • What's the relationship between meta-circular interpreters, virtual machines and increased performance?

    - by Gomi
    I've read about meta-circular interpreters on the web (including SICP) and I've looked into the code of some implementations (such as PyPy and Narcissus). I've read quite a bit about two languages which made great use of metacircular evaluation, Lisp and Smalltalk. As far as I understood Lisp was the first self-hosting compiler and Smalltalk had the first "true" JIT implementation. One thing I've not fully understood is how can those interpreters/compilers achieve so good performance or, in other words, why is PyPy faster than CPython? Is it because of reflection? And also, my Smalltalk research led me to believe that there's a relationship between JIT, virtual machines and reflection. Virtual Machines such as the JVM and CLR allow a great deal of type introspection and I believe they make great use it in Just-in-Time (and AOT, I suppose?) compilation. But as far as I know, Virtual Machines are kind of like CPUs, in that they have a basic instruction set. Are Virtual Machines efficient because they include type and reference information, which would allow language-agnostic reflection? I ask this because many both interpreted and compiled languages are now using bytecode as a target (LLVM, Parrot, YARV, CPython) and traditional VMs like JVM and CLR have gained incredible boosts in performance. I've been told that it's about JIT, but as far as I know JIT is nothing new since Smalltalk and Sun's own Self have been doing it before Java. I don't remember VMs performing particularly well in the past, there weren't many non-academic ones outside of JVM and .NET and their performance was definitely not as good as it is now (I wish I could source this claim but I speak from personal experience). Then all of a sudden, in the late 2000s something changed and a lot of VMs started to pop up even for established languages, and with very good performance. Was something discovered about the JIT implementation that allowed pretty much every modern VM to skyrocket in performance? A paper or a book maybe?

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  • What would be a good opensource software for graphing circles, circular regions, and regions bounded by curves and/or arcs?

    - by Michael Dykes
    Hullo all. I have just started s job with Chegg, and my 1st assignment has me writign solutions for Stewart's Essential Calculus. I am dealing with the chapter on multiple integration, and need a good open-source software that I can easily use to draw regions (domains) that would require multiple integrals: i.e. circular regions, portions of circles, regions bounded by curves and/or arcs, and at some point 3D pictures. In most of these cases, I am not working with an exact equation or perhaps need to draw the region bounded by r (radius) between 1 and 2, and the angle theta bounded between pi/4 and 3 pi/4. I am not too terribly familiar with programs like Corel Draw, but the documents I have from this company suggest Corel Draw. So I think I am looking for an open-source free program like Corel Draw or something similar. Any additional suggestions would also be appreciated. I know I can do most, if not all of this using TikZ, but the learning curve is a bit steep, and at the moment I an on a time constraint. Thanks.

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  • Is there a way to morph / convert a circular sprite into a square programmatically?

    - by John
    I have a sprite which is basically just an image of a circle and some content inside. Is there a way that I can programmatically stretch / distort it into something like: I don't care so much about the distortion. The original circular image is 100x100px, and the modified image should also be 100x100px. So its really the content that is being distorted. Can this be done using shaders or some other programmatic way ? The initial circular image is most likely determined at run time, which is why I need to programmatically convert the circular sprite to square. Please do not edit the tags, as the question applies to both versions of cocos2d (iPhone & x), and the solution will most likely work in both regardless of whether one uses C or C++ since the apis are similar, and OpenGL commands work similarly.

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  • Do NOT Change "Copy Local” project references to false, unless understand subsequences.

    - by Michael Freidgeim
    To optimize performance of visual studio build I've found multiple recommendations to change CopyLocal property for dependent dlls to false,e.g. From http://stackoverflow.com/questions/690033/best-practices-for-large-solutions-in-visual-studio-2008 CopyLocal? For sure turn this offhttp://stackoverflow.com/questions/280751/what-is-the-best-practice-for-copy-local-and-with-project-referencesAlways set the Copy Local property to false and enforce this via a custom msbuild stephttp://codebetter.com/patricksmacchia/2007/06/20/benefit-from-the-c-and-vb-net-compilers-perf/BenefitBenefitMy advice is to always set ‘Copy Local’ to falseSome time ago we've tried to change the setting to false, and found that it causes problem for deployment of top-level projects.Recently I've followed the suggestion and changed the settings for middle-level projects. It didn't cause immediate issues, but I was warned by Readify Consultant Colin Savage about possible errors during deploymentsI haven't undone the changes immediately and we found a few issues during testing.There are many scenarios, when you need to have Copy Local’ left to True.The concerns are highlighted in some stack overflow answers, but they have small number of votes.Top-level projects:  set copy local = true.First of all, it doesn't work correctly for top-level projects, i.e. executables or web sites.As pointed in the answer http://stackoverflow.com/a/6529461/52277for all the references in the one at the top set copy local = true.Alternatively you have to change output directory as it's described in http://www.simple-talk.com/dotnet/.net-framework/partitioning-your-code-base-through-.net-assemblies-and-visual-studio-projects/If you set ‘ Copy Local = false’, VS will, unless you tell it otherwise, place each assembly alone in its own .\bin\Debugdirectory. Because of this, you will need to configure VS to place assemblies together in the same directory. To do so, for each VS project, go to VS > Project Properties > Build tab > Output path, and set the Ouput path to ..\bin\Debugfor debug configuration, and ..\bin\Release for release configuration.Second-level  dependencies:  set copy local = true.Another example when copylocal =false fails on run-time, is when top level assembly doesn't directly referenced one of indirect dependencies.E..g. Top-level assembly A has reference to assembly B with copylocal =true, but assembly B has reference to assembly C with copylocal =false. Most likely assembly C will be missing on runtime and will cause errors E.g. http://stackoverflow.com/questions/602765/when-should-copy-local-be-set-to-true-and-when-should-it-not?lq=1Copy local is important for deployment scenarios and tools. As a general rule you should use CopyLocal=True and http://stackoverflow.com/questions/602765/when-should-copy-local-be-set-to-true-and-when-should-it-not?lq=1 Unfortunately there are some quirks and CopyLocal won't necessary work as expected for assembly references in secondary assemblies structured as shown below.MainApp.exe MyLibrary.dll ThirdPartyLibrary.dll (if in the GAC CopyLocal won't copy to MainApp bin folder)This makes xcopy deployments difficult . .Reflection called DLLs  dependencies:  set copy local = true.E.g user can see error "ISystem.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information."The fix for the issue is recommended in http://stackoverflow.com/a/6200173/52277"I solved this issue by setting the Copy Local attribute of my project's references to true."In general, the problems with investigation of deployment issues may overweight the benefits of reduced build time. Setting the Copy Local to false without considering deployment issues is not a good idea.

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  • C# - Removing items from lists and all references to them.

    - by LiamV
    Hi there, I'm facing a situation where I have dependent objects and I would like to be able to remove an object and all references to it. Say I have an object structure like the code below, with a Branch type which references two Nodes. public class Node { // Has Some Data! } public class Branch { // Contains references to Nodes public Node NodeA public Node NodeB } public class Graph { public List<Node> Nodes; public List<Branch> Branches; } If I remove a Node from the Nodes list in the Graph class, it is still possible that one or more Branch objects still contains a reference to the removed Node, thus retaining it in memory, whereas really what I would quite like would be to set any references to the removed Node to null and let the garbage collection kick in. Other than enumerating through each Branch and checking each Node reference sequentially, are there any smart ideas on how I remove references to the Node in each Branch instance AND indeed any other class which reference the removed Node? Much appreciated, Liam

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  • Removing items from lists and all references to them.

    - by LiamV
    I'm facing a situation where I have dependent objects and I would like to be able to remove an object and all references to it. Say I have an object structure like the code below, with a Branch type which references two Nodes. public class Node { // Has Some Data! } public class Branch { // Contains references to Nodes public Node NodeA public Node NodeB } public class Graph { public List<Node> Nodes; public List<Branch> Branches; } If I remove a Node from the Nodes list in the Graph class, it is still possible that one or more Branch objects still contains a reference to the removed Node, thus retaining it in memory, whereas really what I would quite like would be to set any references to the removed Node to null and let the garbage collection kick in. Other than enumerating through each Branch and checking each Node reference sequentially, are there any smart ideas on how I remove references to the Node in each Branch instance AND indeed any other class which reference the removed Node?

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  • What are the consequences of immutable classes with references to mutable classes?

    - by glenviewjeff
    I've recently begun adopting the best practice of designing my classes to be immutable per Effective Java [Bloch2008]. I have a series of interrelated questions about degrees of mutability and their consequences. I have run into situations where a (Java) class I implemented is only "internally immutable" because it uses references to other mutable classes. In this case, the class under development appears from the external environment to have state. Do any of the benefits (see below) of immutable classes hold true even by only "internally immutable" classes? Is there an accepted term for the aforementioned "internal mutability"? Wikipedia's immutable object page uses the unsourced term "deep immutability" to describe an object whose references are also immutable. Is the distinction between mutability and side-effect-ness/state important? Josh Bloch lists the following benefits of immutable classes: are simple to construct, test, and use are automatically thread-safe and have no synchronization issues do not need a copy constructor do not need an implementation of clone allow hashCode to use lazy initialization, and to cache its return value do not need to be copied defensively when used as a field make good Map keys and Set elements (these objects must not change state while in the collection) have their class invariant established once upon construction, and it never needs to be checked again always have "failure atomicity" (a term used by Joshua Bloch) : if an immutable object throws an exception, it's never left in an undesirable or indeterminate state

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  • Two classes and inline functions

    - by klew
    I have two classes and both of them uses some of the other class, on example: // class1.h class Class1; #include "class2.h" class Class1 { public: static Class2 *C2; ... }; // class2.h class Class2; #include "class1.h" class Class2 { public: static Class1 *C1; ... }; And when I define it like in example above, it works (I also have some #ifndef to avoid infinite header recurency). But I also want to add some inline functions to my classes. And I read here that I should put definition of inline function in header file, because it won't work if I'll put them in cpp file and want to call them from other cpp file (when I do it I get undefined reference during linking). But the problem here is with something like this: // class1.h ... inline void Class1::Foo() { C2->Bar(); } I get error: invalid use of incomplete type ‘struct Class2’. So how can I do it?

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  • 2 Classes need each other declared C++

    - by Prodigga
    I have a "Game" class which holds all the games settings and manages the game. I have a "Grid" class which is the grid the game is played on. The "Game" class initializes a "Grid" object as one of its members (passing itself ("this") as one of the parameters for "Grid"s constructor).. The "Grid" object therefor needs to deal with a "Game*" pointer. To do this it needs to know what "Game" is; i need to declare it before "Grid". But "Game" uses "Grid"...so it also needs "Grid" declared before it. so confused on how to include headers/etc correctly here..

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