dynamic class loaders - Page 58

Class Versus Struct

- by Prometheus87

In C++ and other influenced languages there is a construct called Structure (struct) and we all know the class. Both are capable of holding functions and variables. some differences are 1. Class is given memory in heap and struct is given memory in stack 2. in class variable are private by default and in struct thy are public My question is that struct was somehow abandoned for Class. Why? other that abstraction, a struct can do all the same stuff a class does. Then why abandon it?

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does class reference itself static anti pattern in prism

- by Michael Riva

I have an application and my desing approach look like this: class Manager { public int State; static Manager _instance = null; public static Manager Instance { get { return _instance; } set { if (_instance == value) return; _instance = value; } } public Manager() { State = 0; Instance=this; } } class Module1 { public void GetState() { Console.WriteLine(Manager.Instance.State); } } class Module2 { public void GetState() { Console.WriteLine(Manager.Instance.State); } } class Module3 { public void GetState() { Console.WriteLine(Manager.Instance.State); } } Manager class already registered in Bootstrapper like : protected override void ConfigureContainer() { base.ConfigureContainer(); Container.RegisterType<Manager>(new ContainerControlledLifetimeManager()); } protected override void InitializeModules() { Manager man= Container.Resolve<Manager>(); } Question is do I need to define my manager object as static in its field to be able to reach its state? Or this is anti pattern or bad for performance?

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Passing class names or objects?

- by nischayn22

I have a switch statement switch ( $id ) { case 'abc': return 'Animal'; case 'xyz': return 'Human'; //many more } I am returning class names,and use them to call some of their static functions using call_user_func(). Instead I can also create a object of that class, return that and then call the static function from that object as $object::method($param) switch ( $id ) { case 'abc': return new Animal; case 'xyz': return new Human; //many more } Which way is efficient? To make this question broader : I have classes that have mostly all static methods right now, putting them into classes is kind of a grouping idea here (for example the DB table structure of Animal is given by class Animal and so for Human class). I need to access many functions from these classes so the switch needs to give me access to the class

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How to flag a class as under development in Java

- by Usavich

I'm working on a internship project, but I have to leave before I can finish up everything. I have 1 class that is not stable enough for production use. I want to mark/flag this class so that other people will not accidentally use it in production. I have already put the notice in Javadoc, but that doesn't seem enough. Some compiler error or warning would be better. The code is organized like this: [Package] | company.foo.bar.myproject |-- Class1.java |-- Class2.java |-- Class3.java <--(not stable) If there was a single factory class that calls those classes in public methods, I could have set the method to class3 as private. However the API is NOT exposed that way. Users will directly use those class, e.g. new Class1();, but I can't make a top-level class private. What's the best practice to deal with this situation?

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How to access variables of uninitialized class?

- by oringe

So I've gone with a somewhat singleton approach to my game class: #include "myGame.h" int main () { myGame game; return game.Execute(); } But now I need to define a class that accesses variables in the instance of myGame. class MotionState { public: virtual void setWorldTransform (...) { VariableFromMyGameClass++; //<-- !? ...} }; I'm trying to integrate this class into my project from an example that just uses globals. How can I access variables of myGame class in the definition of new classes? Should I give up on my singleton approach?

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How to map hash keys to methods for an encapsulated Ruby class (tableless model)?

- by user502052

I am using Ruby on Rails 3 and I am tryng to map a hash (key, value pairs) to an encapsulated Ruby class (tableless model) making the hash key as a class method that returns the value. In the model file I have class Users::Account #< ActiveRecord::Base def initialize(attributes = {}) @id = attributes[:id] @firstname = attributes[:firstname] @lastname = attributes[:lastname] end end def self.to_model(account) JSON.parse(account) end My hash is hash = {\"id\":2,\"firstname\":\"Name_test\",\"lastname\":\"Surname_test\"} I can make account = Users::Account.to_model(hash) that returns (debugging) --- id: 2 firstname: Name_test lastname: Surname_test That works, but if I do account.id I get this error NoMethodError in Users/accountsController#new undefined method `id' for #<Hash:0x00000104cda410> I think because <Hash:0x00000104cda410> is an hash (!) and not the class itself. Also I think that doing account = Users::Account.to_model(hash) is not the right approach. What is wrong? How can I "map" those hash keys to class methods?

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How do I dynamically instantiate a class in javascript?

- by Adam

I'm starting out with classes in Javascript and have hit a wall. I've looked all over for a tutorial that goes a little further than simply how to construct a class (usually Animal) then extend the class and have a Method do something (Dog alert('Bark');). I have created a class that I want a user to be able to instantiate (is that the right word)? For example the first stage in my program is for the user to give the class a name, and then start to populate the various variables in the class. When they've done that they may do it again many times. So if: var className = new MyObject(); How do I dynamically create the name of the new object className and then refer to it later in the code?

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Is it ok to dynamic cast "this" as a return value?

- by Panayiotis Karabassis

This is more of a design question. I have a template class, and I want to add extra methods to it depending on the template type. To practice the DRY principle, I have come up with this pattern (definitions intentionally omitted): template <class T> class BaseVector: public boost::array<T, 3> { protected: BaseVector<T>(const T x, const T y, const T z); public: bool operator == (const Vector<T> &other) const; Vector<T> operator + (const Vector<T> &other) const; Vector<T> operator - (const Vector<T> &other) const; Vector<T> &operator += (const Vector<T> &other) { (*this)[0] += other[0]; (*this)[1] += other[1]; (*this)[2] += other[2]; return *dynamic_cast<Vector<T> * const>(this); } } template <class T> class Vector : public BaseVector<T> { public: Vector<T>(const T x, const T y, const T z) : BaseVector<T>(x, y, z) { } }; template <> class Vector<double> : public BaseVector<double> { public: Vector<double>(const double x, const double y, const double z); Vector<double>(const Vector<int> &other); double norm() const; }; I intend BaseVector to be nothing more than an implementation detail. This works, but I am concerned about operator+=. My question is: is the dynamic cast of the this pointer a code smell? Is there a better way to achieve what I am trying to do (avoid code duplication, and unnecessary casts in the user code)? Or am I safe since, the BaseVector constructor is private?

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Django: Can class-based views accept two forms at a time?

- by Hooman

If I have two forms: class ContactForm(forms.Form): name = forms.CharField() message = forms.CharField(widget=forms.Textarea) class SocialForm(forms.Form): name = forms.CharField() message = forms.CharField(widget=forms.Textarea) and wanted to use a class based view, and send both forms to the template, is that even possible? class TestView(FormView): template_name = 'contact.html' form_class = ContactForm It seems the FormView can only accept one form at a time. In function based view though I can easily send two forms to my template and retrieve the content of both within the request.POST back. variables = {'contact_form':contact_form, 'social_form':social_form } return render(request, 'discussion.html', variables) Is this a limitation of using class based view (generic views)? Many Thanks

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Why does this code generate an error? [closed]

- by user559601

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Why doesn't C++ allow you to request a pointer to the most derived class?

- by Matthew Lowe

(This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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Difference between Class Abstraction and Object Interfaces in PHP?

- by Mark Tomlin

What is the difference between a Class Abstraction and an Object Interfaces in PHP? I ask because, I don't really see the point to both of them, they both do the same thing! So, what are the advantages of disadvantages using both against one or the other? Class Abstraction: abstract class aClass { // Force extending class to define these methods abstract public function setVariable($name, $var); abstract public function getHtml($template); } Object Interface: interface iClass { // Force impementing class to define these methods public function setVariable($name, $var); public function getHtml($template); }

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Can pydoc/help() hide the documentation for inherited class methods and attributes?

- by EOL

When declaring a class that inherits from a specific class: class C(dict): added_attribute = 0 the documentation for class C lists all the methods of dict (either through help(C) or pydoc). Is there a way to hide the inherited methods from the automatically generated documentation (the documentation string can refer to the base class, for non-overwritten methods)? or is it impossible? This would be useful: pydoc lists the functions defined in a module after its classes. Thus, when the classes have a very long documentation, a lot of less than useful information is printed before the new functions provided by the module are presented, which makes the documentation harder to exploit (you have to skip all the documentation for the inherited methods until you reach something specific to the module being documented).

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Coarse Collision Detection in highly dynamic environment

- by Millianz

I'm currently working a 3D space game with A LOT of dynamic objects that are all moving (there is pretty much no static environment). I have the collision detection and resolution working just fine, but I am now trying to optimize the collision detection (which is currently O(N^2) -- linear search). I thought about multiple options, a bounding volume hierarchy, a Binary Spatial Partitioning tree, an Octree or a Grid. I however need some help with deciding what's best for my situation. A grid seems unfeasible simply due to the space requirements and cache coherence problems. Since everything is so dynamic however, it seems to be that trees aren't ideal either, since they would have to be completely rebuilt every frame. I must admit I never implemented a physics engine that required spatial partitioning, do I indeed need to rebuild the tree every frame (assuming that everything is constantly moving) or can I update the trees after integrating? Advice is much appreciated - to give some more background: You're flying a space ship in an asteroid field, and there are lots and lots of asteroids and some enemy ships, all of which shoot bullets. EDIT: I came across the "Sweep an Prune" algorithm, which seems like the right thing for my purposes. It appears like the right mixture of fast building of the data structures involved and detailed enough partitioning. This is the best resource I can find: http://www.codercorner.com/SAP.pdf If anyone has any suggestions whether or not I'm going in the right direction, please let me know.

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A new mission statement for my school's algorithms class

- by Eric Fode

The teacher at Eastern Washington University that is now teaching the algorithms course is new to eastern and as a result the course has changed drastically mostly in the right direction. That being said I feel that the class could use a more specific, and industry oriented (since that is where most students will go, though suggestions for an academia oriented class are also welcome) direction, having only worked in industry for 2 years I would like the community's (a wider and much more collectively experienced and in the end plausibly more credible) opinion on the quality of this as a statement for the purpose an algorithms class, and if I am completely off target your suggestion for the purpose of a required Jr. level Algorithms class that is standalone (so no other classes focusing specifically on algorithms are required). The statement is as follows: The purpose of the algorithms class is to do three things: Primarily, to teach how to learn, do basic analysis, and implement a given algorithm found outside of the class. Secondly, to teach the student how to model a problem in their mind so that they can find a an existing algorithm or have a direction to start the development of a new algorithm. Third, to overview a variety of algorithms that exist and to deeply understand and analyze one algorithm in each of the basic algorithmic design strategies: Divide and Conquer, Reduce and Conquer, Transform and Conquer, Greedy, Brute Force, Iterative Improvement and Dynamic Programming. The Question in short is: do you agree with this statement of the purpose of an algorithms course, so that it would be useful in the real world, if not what would you suggest?

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How-to get the binding for a tab in the Dynamic Tab Shell Template

- by Frank Nimphius

The Dynamic Tab Shell template does expose a method on the Tab.java class that allows you to get access to the ADF binding container for a tab. At least in theory this works, because in practice this call always returns a null value (a bug is filed for this). To work around the problem, you can use code similar to the following to get the ADF binding for a specific tab DCBindingContainer currentBinding = (DCBindingContainer) BindingContext.getCurrent().getCurrentBindingsEntry(); DCBindingContainer templateBinding = (DCBindingContainer)currentBinding.get("ptb1"); DCBindingContainer tabBinding= (DCBindingContainer)templateBinding.get("r"+0); In the code line above, the tabBinding variable will hold the binding reference to the first tab in the dynamic tab shell template. Note that the tab doesn't need to be visible for this (which has to do with how the template works). "ptb1" is the template reference name in the PageDef file (Executable section) of the template consumer view. Check this string in your page before using this code. If it differs, change it also in the code above. "r0" is the binding reference of the first tab in the template. Te last tab is referenced by "r14".

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Calling a .NET C# class from XSLT

- by HanSolo

If you've ever worked with XSLT, you'd know that it's pretty limited when it comes to its programming capabilities. Try writing a for loop in XSLT and you'd know what I mean. XSLT is not designed to be a programming language so you should never put too much programming logic in your XSLT. That code can be a pain to write and maintain and so it should be avoided at all costs. Keep your xslt simple and put any complex logic that your xslt transformation requires in a class. Here is how you can create a helper class and call that from your xslt. For example, this is my helper class: public class XsltHelper { public string GetStringHash(string originalString) { return originalString.GetHashCode().ToString(); } } And this is my xslt file(notice the namespace declaration that references the helper class): <?xml version="1.0" encoding="UTF-8" ?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns:ext="http://MyNamespace"> <xsl:output method="text" indent="yes" omit-xml-declaration="yes"/> <xsl:template match="/">The hash code of "<xsl:value-of select="stringList/string1" />" is "<xsl:value-of select="ext:GetStringHash(stringList/string1)" />". </xsl:template> </xsl:stylesheet> Here is how you can include the helper class as part of the transformation: string xml = "<stringList><string1>test</string1></stringList>"; XmlDocument xmlDocument = new XmlDocument(); xmlDocument.LoadXml(xml); XslCompiledTransform xslCompiledTransform = new XslCompiledTransform(); xslCompiledTransform.Load("XSLTFile1.xslt"); XsltArgumentList xsltArgs = new XsltArgumentList(); xsltArgs.AddExtensionObject("http://MyNamespace", Activator.CreateInstance(typeof(XsltHelper))); using (FileStream fileStream = new FileStream("TransformResults.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite)) { // transform the xml and output to the output file ... xslCompiledTransform.Transform(xmlDocument, xsltArgs, fileStream); }

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Updating entities in response to collisions - should this be in the collision-detection class or in the entity-updater class?

- by Prog

In a game I'm working on, there's a class responsible for collision detection. It's method detectCollisions(List<Entity> entities) is called from the main gameloop. The code to update the entities (i.e. where the entities 'act': update their positions, invoke AI, etc) is in a different class, in the method updateEntities(List<Entity> entities). Also called from the gameloop, after the collision detection. When there's a collision between two entities, usually something needs to be done. For example, zero the velocity of both entities in the collision, or kill one of the entities. It would be easy to have this code in the CollisionDetector class. E.g. in psuedocode: for(Entity entityA in entities){ for(Entity entityB in entities){ if(collision(entityA, entityB)){ if(entityA instanceof Robot && entityB instanceof Robot){ entityA.setVelocity(0,0); entityB.setVelocity(0,0); } if(entityA instanceof Missile || entityB instanceof Missile){ entityA.die(); entityB.die(); } } } } However, I'm not sure if updating the state of entities in response to collision should be the job of CollisionDetector. Maybe it should be the job of EntityUpdater, which runs after the collision detection in the gameloop. Is it okay to have the code responding to collisions in the collision detection system? Or should the collision detection class only detect collisions, report them to some other class and have that class affect the state of the entities?

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Dynamic Monitoring Service (DMS) Configuration Dumping and CPU Utilization

- by ShawnBailey

There was recently a report of CPU spikes on a system that were occuring at precise 3 hour intervals. Research revealed that the spikes were the result of the Dynamic Monitoring Service generating a metrics dump and writing it under the server 'logs' folder for every WLS server in the domain. This blog provides some information on what this is for and how to control it. The Dynamic Monitoring Service is a facility in FMw (JRF to be more precise) that collects runtime data on the components deployed to WebLogic. Each component is responsible for how much or how little they use the service and SOA collects a fair amount of information. To view what is collected on any running server you can use the following URL, http://host:port/dms/Spy and login with admin credentials. DMS is essentially always running and collecting this information in the runtime and to protect against loss of this data it also runs automatic backups, by default at the 3 hour interval mentioned above. Most of the management options for DMS are exposed through WLST but these settings are not so we must open the dms_config.xml file which can be found in DOMAIN_HOME/config/fmwconfig/servers/<server_name>/dms_config.xml. The contents are fairly short and at the bottom you will find the following entry: <dumpConfiguration> <dump intervalSeconds="10800" maxSizeMBytes="75" enabled="true"/> </dumpConfiguration> The interval of 10800 seconds corresponds to the 3 hours and the maximum size is 75MB. The file is written as an archive to DOMAIN_HOME/servers/<server_name>/logs/metrics. This archive contains the dump in XML format. You can disable the dumps all together by simply setting the 'enabled' value to 'false' or of course you could modify the other parameters to suit your needs. Disabling the dumps will NOT impact DMS collections or display at runtime. It will only eliminate these periodic backups.

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Class Decorators, Inheritence, super(), and maximum recursion

- by jamstooks

I'm trying to figure out how to use decorators on subclasses that use super(). Since my class decorator creates another subclass a decorated class seems to prevent the use of super() when it changes the className passed to super(className, self). Below is an example: def class_decorator(cls): class _DecoratedClass(cls): def __init__(self): return super(_DecoratedClass, self).__init__() return _DecoratedClass class BaseClass(object): def __init__(self): print "class: %s" % self.__class__.__name__ def print_class(self): print "class: %s" % self.__class__.__name__ bc = BaseClass().print_class() class SubClass(BaseClass): def print_class(self): super(SubClass, self).print_class() sc = SubClass().print_class() @class_decorator class SubClassAgain(BaseClass): def print_class(self): super(SubClassAgain, self).print_class() sca = SubClassAgain() # sca.print_class() # Uncomment for maximum recursion The output should be: class: BaseClass class: BaseClass class: SubClass class: SubClass class: _DecoratedClass Traceback (most recent call last): File "class_decorator_super.py", line 34, in <module> sca.print_class() File "class_decorator_super.py", line 31, in print_class super(SubClassAgain, self).print_class() ... ... RuntimeError: maximum recursion depth exceeded while calling a Python object Does anyone know of a way to not break a subclass that uses super() when using a decorator? Ideally I'd like to reuse a class from time to time and simply decorate it w/out breaking it.

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Adding a class to the $tag surrounding a <label> in a Zend_Form with the Label decorator

- by Roderik

I'm trying to get the following html out of Zend_Form <div class="group wat-cf"> <div class="left"> <label class="label right">Username</label> </div> <div class="right"> <input type="text" class="text_field"> </div> </div> Using the following code: $username->setAttrib("class", "text_field") ->setDecorators(array( 'ViewHelper', 'Description', 'Errors', array(array('data'=>'HtmlTag'), array('tag' => 'div', 'class' => 'right')), array('Label', array('tag' => 'div', 'class' => 'label right')), array(array('row'=>'HtmlTag'),array('tag'=>'div', 'class' => 'group wat-cf')) )); I can get the next fragment <div class="group wat-cf"> <div id="username-label"> <label for="username" class="label right required">Username:</label> </div> <div class="right"> <input type="text" name="username" id="username" value="" class="text_field"> </div> </div> so apart from some extra id's and required classes i don't mind, i need to get a class "left" on div id="username-label" Now adding class to the Label line, gets the class added on the element. I also don't see and option to do this in the Label decorator code itself. So i need a custom Label decorator, or is there some other way i'm missing?

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How do I access abstract private data from derived class without friend or 'getter' functions in C++?

- by John

So, I am caught up in a dilemma right now. How am I suppose to access a pure abstract base class private member variable from a derived class? I have heard from a friend that it is possible to access it through the base constructor, but he didn't explain. How is it possible? There are some inherited classes from base class. Is there any way to gain access to the private variables ? class Base_button { private: bool is_vis; Rect rButton; public: // Constructors Base_button(); Base_button( const Point &corner, double height, double width ); // Destructor virtual ~ Base_button(); // Accessors virtual void draw() const = 0; bool clicked( const Point &click ) const; bool is_visible() const; // Mutators virtual void show(); virtual void hide(); void move( const Point &loc ); }; class Button : public Base_button { private: Message mButton; public: // Constructors Button(); Button( const Point &corner, const string &label ); // Acessors virtual void draw() const; // Mutators virtual void show(); virtual void hide(); }; I want to be able access Rect and bool in the base class from the subclass

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templated method on T inside a templated class on TT : Is that possible/correct.

- by paercebal

I have a class MyClass which is templated on typename T. But inside, I want a method which is templated on another type TT (which is unrelated to T). After reading/tinkering, I found the following notation: template <typename T> class MyClass { public : template<typename TT> void MyMethod(const TT & param) ; } ; For stylistic reasons (I like to have my templated class declaration in one header file, and the method definitions in another header file), I won't define the method inside the class declaration. So, I have to write it as: template <typename T> // this is the type of the class template <typename TT> // this is the type of the method void MyClass<T>::MyMethod(const TT & param) { // etc. } I knew I had to "declare" the typenames used in the method, but didn't know how exactly, and found through trials and errors. The code above compiles on Visual C++ 2008, but: Is this the correct way to have a method templated on TT inside a class templated on T? As a bonus: Are there hidden problems/surprises/constraints behind this kind of code? (I guess the specializations can be quite amusing to write)

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Can a grails controller extend from a base class? How to make it so grails doesn't blow up?

- by egervari

I wrote a base class to help build my controllers more quickly and to remove duplication. It provides some helper methods, default actions and some meta programming to make these things easier to build. One of those methods in the base class is like this: def dynamicList(Class clazz) { def model = new LinkedHashMap() model[getMapString(clazz) + "s"] = list(clazz) model[getMapString(clazz) + "sTotal"] = count(clazz) model } The action that calls it, also in the base class, is this: def list = { dynamicList(clazz) } Unfortunately, when I go to list action in the controller subclass that inherits the base class when my application is deployed, I get this exception: groovy.lang.MissingMethodException: No signature of method: groovy.lang.MissingMethodException.dynamicList() is applicable for argument types: (java.lang.Class) values: [class project .user.User] at project.user.UserController$_closure1.doCall(UserController.groovy:18) at project.user.UserController$_closure1.doCall(UserController.groovy) at java.lang.Thread.run(Thread.java:619) How can I hit grails over the head and just tell it do what I want it to do? My controller unit tests run just fine, so grails' run-time is totally at fault :/ Ken

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How to deal with class composition when components cannot be accessed from the outside?

- by Chathuranga

For example if I say I have three classes A, B, and C where B and C have a composition relation ship with A. That means the life of B and C is handled by A, and also B and C cannot access directly from the outside. For some reason my DataService class needs to return objects of B and C as It cant return a object of A as B and C cannot be initialized at the same time. (to be able to initializeC you have to initializeB first). So that I'm returning DataTables from DataService and then inside the class A those data tables are converted to B / C objects. If B and C objects cannot be initialized at the same time is it valid to say that B and C have a composition relationship with A? If its composition is it must to generate A with B and C inside? What is the proper way to handle this sort of a problem? EDIT: Following code explains the way I'm doing it now with DataTables. Example: class A { private List<B> B; private List <C> C; public A() { B= new List<B>(); C= new List<C>(); } public List<B> GetB( DataTable dt) { // Create a B list from dt return B; } } class Presenter { private void Show B() { _View.DataGrid = A.GetB(DataService.GetAListOfB()); } } The actual scenario is I have a class called WageInfo and classes Earning and Deduction having a composition relationship in the design. But for you to generate Deductions first you should Generate earnings and should be saved in a table. Then only you can generate deductions for the earnings to calculate balance wages. Also note that these contained classes have a one to many relationship with the containing class WageInfo. So actually WageInfo has a List<Earnings> and List<Deduction> My initial question was, is it ok if my DataService class returns Deductions / Earnings objects (actually lists) not a WageInfo? Still not clear?

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