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  • In Ruby or Python can the very idea of Class be rewritten?

    - by John Berryman
    Howdy All... first time at stack overflow. I'm looking into using some of the metaprogramming features provided by Ruby or Python, but first I need to know the extent to which they will allow me to extend the language. The main thing I need to be able to do is to rewrite the concept of Class. This doesn't mean that I want to rewrite a specific class during run time, but rather I want to make my own conceptualization of what a Class is. To be a smidge more specific here, I want to make something that is like what people normally call a Class, but I want to follow an "open world" assumption. In the "closed world" of normal Classes, if I declare Poodle to be a subclass of Dog to be a subclass of Animal, then I know that Poodle is not going to also be a type of FurCoat. However, in an open world Class, then the Poodle object I've defined may or may not be and object of type FurCoat and we won't know for sure until I explain that I can wear the poodle. (Poor poodle.) This all has to do with a study I'm doing concerning OWL ontologies. Just so you know, I've tried to find information online, but due to the overloading of terms here I haven't found anything helpful. Super thanks, John

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  • PHP: Class extends problem "Call to private method ... from context ..."

    - by sombe
    I have 3 classes in WordPress (the question itself is unrelated to it): class WP_Widget class Theme_Widget extends WP_Widget class Specific_Widget extends Theme_Widget Essentially Theme_Widget contains some extension functions to the basic WP_Widget. Inside Specific_Widget I call one of Theme_Widget's methods: class Specific_Widget { function __construct() { $this->some_method_that_belongs_to_Theme_Widget(); } } When I instantiate Specific_Widget, PHP throws a fatal error as follows: Fatal error: Call to private method Theme_Widget::some_method_that_belongs_to_Theme_Widget() from context 'Specific_Widget' in ... Do you have an idea as to how I can resolve this? This is the first time I've received this error from PHP. Could it be derive from WordPress itself?

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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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  • Are reference attributes destroyed when class is destroyed in C++?

    - by Genba
    Suppose I have a C++ class with an attribute that is a reference: class ClassB { ClassA &ref; public: ClassB(ClassA &_ref); } Of course, the constructor is defined this way: ClassB::ClassB(ClassA &_ref) : ref(_ref) { /* ... */ } My question is: When an instance of class 'ClassB' is destroyed, is the object referenced by 'ClassB::ref' also destroyed?

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  • Can I use an abstract class instead of a private __construct() when creating a singleton in PHP?

    - by Pheter
    When creating a Singleton in PHP, I ensure that it cannot be instantiated by doing the following: class Singleton { private function __construct() {} private function __clone() {} public static function getInstance() {} } However, I realised that defining a class as 'abstract' means that it cannot be instantiated. So is there anything wrong with doing the following instead: abstract class Singleton { public static function getInstance() {} } The second scenario allows me to write fewer lines of code which would be nice. (Not that it actually makes much of a difference.)

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  • Adding a first and last class to Wordpress' widget contents

    - by user571188
    In Wordpress, I'm looking for some way to add a "last" and a "first" class to list items inside Wordpress widgets. The HTML could look like this: <div class="widget-area"> <ul > <li class="widget_recent_comments"> <h3 class="widget-title">Recent comments</h3> <ul id="recentcomments"> <li class="recentcomments">Comment 1</li> <li class="recentcomments">Comment 2</li> <li class="recentcomments">Comment 3</li> <li class="recentcomments">Comment 4</li> </ul> </li> <li class="widget_my_links"> <h3 class="widget-title">My links</h3> <ul id="my-links"> <li class="item">Link 1</li> <li class="item">Link 2</li> <li class="item">Link 3</li> <li class="item">Link 4</li> <li class="item">Link 5</li> </ul> </li> </ul></div> In this example above i'd like to have first/last classes added to the li with "Comment 1", "Comment 4", "Link 1" and "Link 5". Is there an easy workaround for this? (I don't want to do this with javascript) Thank you.

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  • How can I create an instance of a class that I can use is more than one place in c#

    - by user1743574
    So I've been working on a class that details students of a university. I have one button that sets the details to a new instance of a class, and another to check if the student passed, through a method in my Class. The problem is that I create an instance of a class in the first button to add the values from what the user input, but I cannot use the second button to access the instance of the class created in the first button. private void button3_Click(object sender, EventArgs e) { Student student1 = new Student(); label1.Text = student1.text(); if (student1.hasPassed() == true) { passfailtextbox.Text = "Pass"; } else { passfailtextbox.Text = "Fail"; } } private void button1_Click(object sender, EventArgs e) { Student student1 = new Student(); student1.FirstName = firstnamebox.Text; student1.SecondName = secondnamebox.Text; student1.DateofBirth = DateTime.Parse(dobtextbox.Text).Date; student1.Course = coursetextbox.Text; student1.MatriculationNumber = int.Parse(matriculationtextbox.Text); student1.YearMark = double.Parse(yearmarktextbox.Text); } public Boolean hasPassed() { if (YearMark < 40) { return false; } else { return true; } } public string text() { return "Student" + " " + firstname + " " + secondname + " " + course + " " + dob.ToString() + " " + matriculationnumber.ToString() + " " + yearmark.ToString() ; }

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  • Mercurial: Class library that will exist for both .NET 3.5 and 4.0?

    - by Lasse V. Karlsen
    I have a rather big class library written in .NET 3.5 that I'd like to upgrade to make available for .NET 4.0 as well. In that process, I will rip out a lot of old junk, and rewrite some code to better take advantage of the new classes and support in .NET 4.0 (like TPL.) The class libraries will thus diverge, but still be similar enough that some bug-fixes can be done to both in the same manner. How should I best organize this class library in Mercurial? I'm using Kiln (fogbugz) if that matters. I'm thinking: Named branches in one repository, can then transplant any bugfixes from one to the other Unnamed branches in one repository, can also transplant, but I think this will look messy Separate repositories, will have to reimplement the bugfixes (or use a non-mercurial-integraded compare tool to help me) What would you do? (any other alternatives that I haven't though of is welcome as well.) Note that the class libraries will diverge pretty heavily in areas, I have some remnants of old collection-type code that does something similar to Linq that I will remove, and some code that uses it that I will rewrite to use the Linq-methods instead. As such, just copying the project files and using #if NET40..#endif sections is not going to work out. Also, the 3.5 version of the class library will not be getting many new features, mostly just critical bug-fixes, so keeping both versions equally "alive" isn't really necessary. Thus, separate copies of all the files are good enough.

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  • How to align C++ class member names in one column in emacs ?

    - by KotBerbelot
    I would like to align all C++ class member names ( do not confuse with member types ) in one column. Lets look at the example of what we have at entrance: class Foo { public: void method1( ); int method2( ); const Bar * method3( ) const; protected: float m_member; }; and this is what we would like to have at the end: class Foo { public: void method1( ); int method2( ); const Bar * method3( ) const; protected: float m_member; }; So the longest member type declaration defines the column to which class member names will be aligned. How can i perform such transformation in emacs ?

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  • Which Java Web Framework allows Cross-Domain Javascripting (http proxy) ?

    - by snsd
    So just a quick intro, I am starting to explore Vaadin, and it's absolutely perfect. Previously, I was juggling PHP, Perl, Ruby, and Jquery for designing rich client web application. It didn't work out too well, as I've burnt out from trying to fix cross browser issues (aka get-it-to-work-on-IE-damn-it), handling server-side, client-side, and building a robust communication between the two tier had lot of code not related to application logic....by the time I was burnt out, only tiny bit of application logic was implemented. Vaadin seems like the answer to my problem as it only requires Java and built on top of GWT. However, I am curious how I can incorporate Cross-Domain Javascripting ? Back in LAMP environment, I had a CGI proxy script that loaded external URL, and injected JS into the proxy-loaded page. I used the CGI proxy script, as it rendered Javascript of the external URL well. Is there a class or package for Java or a specific Java web framework similiar to Vaadin that makes this possible ? Thank you.

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  • How to get number of attributes in a java class?

    - by llm
    I have a java class containing all the columns of a database table as attributes (member variables) and corresponding getters and setters. I want to have a method in this class called getColumnCount() that returns the number of columns (i.e. the number of attributes in the class)? How would I implement this without hardcoding the number? I am open to critisims on this in general and suggestions. Thanks.

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  • Virtualmin domain name registration php

    - by David Maitland
    in a PHP web page i need to run this following command to create a new domain: virtualmin create-domain --domain DOMAIN --pass PASS --plan 'Standard Package' --limits-from-plan --features-from-plan This is usually executed in a shell but i don't know how to do it from a web page and also i need to take the domain string and pass string from a web form. Can anyone help with the PHP code as my skills are basic and i have already tried a few things that just don't work. Thanks.

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  • What is the point declaring variables at the end of class?

    - by serhio
    I saw multiple examples in MSDN that uses to declare the internal fields at the end of the class. What is the point? I find this a little embarrassing, because each time Visual Studio adds a method it adds it to the end of the class, so there is need every time to move it... class A { public A(){} // Methods, Properties, etc ... private string name; } class A { private string name; public A(){} // Methods, Properties, etc ... }

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  • Is it possible for an abstract class to force it's children to have a constructor in PHP?

    - by Logan Serman
    I would like to do something like this: abstract class Foo { public function __construct() { echo 'This is the parent constructor'; } abstract function __construct(); } class Bar extends Foo { // constructor is required as this class extends Foo public function __construct() { //call parent::__construct() if necessary echo 'This is the child constructor'; } } But I get a fatal error when doing this: Fatal error: Cannot redeclare Foo::__construct() in Foo.php on line 8 Is there another way to ensure child classes have a constructor?

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  • Passing a generic class to a java function?

    - by rodo
    Is it possible to use Generics when passing a class to a java function? I was hoping to do something like this: public static class DoStuff { public <T extends Class<List>> void doStuffToList(T className) { System.out.println(className); } public void test() { doStuffToList(List.class); // compiles doStuffToList(ArrayList.class); // compiler error (undesired behaviour) doStuffToList(Integer.class); // compiler error (desired behaviour) } } Ideally the List.class and ArrayList.class lines would work fine, but the Integer.class line would cause a compile error. I could use Class as my type instead of T extends Class<List> but then I won't catch the Integer.class case above.

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  • how get attribute relation from another entity class Java Persistance API and show to JSP through servlet?

    - by user1787209
    I have 2 entities are entities meeting and meetingAgenda. I write code entity class (EJB) from database like this. public class Meeting implements Serializable { ...... @XmlTransient public Collection<MeetingAgenda> getMeetingAgendaCollection() { return meetingAgendaCollection; } public void setMeetingAgendaCollection(Collection<MeetingAgenda> meetingAgendaCollection) { this.meetingAgendaCollection = meetingAgendaCollection; } ....... } and entity class meeting agenda like this. ..... public class MeetingAgenda implements Serializable { .... public String getAgenda() { return agenda; } public void setAgenda(String agenda) { this.agenda = agenda; } .... } method getMeetingAgendaCollection is a relation from meeting entity . then, in my controller servlet i call EJB like this. public class ControllerServlet extends HttpServlet { @EJB private RapatFacadeLocal rapatFacade; public void init() throws ServletException { // store category list in servlet context getServletContext().setAttribute("meetings", rapatFacade.findAll()); } ...... i want to show data from table entities meeting and meetingAgenda...but i can't.. please help.. i write code in JSP page.. like this.. <c:forEach var="meeting" items="${meetings}"> <td> MeetingCode : ${meeting.meetingCode} </td> <td> Meeting : ${meeting.meeting} </td> <td> Agenda : ${meeting.getMeetingAgendaCollection} </td> </c:forEach> how do I display data Agenda using getMeetingAgendaCollection ???? thanks for your help.

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  • Abstract exception super type

    - by marcof
    If throwing System.Exception is considered so bad, why wasn't Exception made abstract in the first place? That way, it would not be possible to call: throw new Exception("Error occurred."); This would enforce using derived exceptions to provide more details about the error that occurred. For example, when I want to provide a custom exception hierarchy for a library, I usually declare an abstract base class for my exceptions: public abstract class CustomExceptionBase : Exception { /* some stuff here */ } And then some derived exception with a more specific purpose: public class DerivedCustomException : CustomExceptionBase { /* some more specific stuff here */ } Then when calling any library method, one could have this generic try/catch block to directly catch any error coming from the library: try { /* library calls here */ } catch (CustomExceptionBase ex) { /* exception handling */ } Is this a good practice? Would it be good if Exception was made abstract? EDIT : My point here is that even if an exception class is abstract, you can still catch it in a catch-all block. Making it abstract is only a way to forbid programmers to throw a "super-wide" exception. Usually, when you voluntarily throw an exception, you should know what type it is and why it happened. Thus enforcing to throw a more specific exception type.

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  • Don't Use "Static" in C#?

    - by Joshiatto
    I submitted an application I wrote to some other architects for code review. One of them almost immediately wrote me back and said "Don't use "static". You can't write automated tests with static classes and methods. "Static" is to be avoided." I checked and fully 1/4 of my classes are marked "static". I use static when I am not going to create an instance of a class because the class is a single global class used throughout the code. He went on to mention something involving mocking, IOC/DI techniques that can't be used with static code. He says it is unfortunate when 3rd party libraries are static because of their un-testability. Is this other architect correct? update: here is an example: APIManager - this class keeps dictionaries of 3rd party APIs I am calling along with the next allowed time. It enforces API usage limits that a lot of 3rd parties have in their terms of service. I use it anywhere I am calling a 3rd party service by calling Thread.Sleep(APIManager.GetWait("ProviderXYZ")); before making the call. Everything in here is thread safe and it works great with the TPL in C#.

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  • Use a custom value object or a Guid as an entity identifier in a distributed system?

    - by Kazark
    tl;dr I've been told that in domain-driven design, an identifier for an entity could be a custom value object, i.e. something other than Guid, string, int, etc. Can this really be advisable in a distributed system? Long version I will invent an situation analogous to the one I am currently facing. Say I have a distributed system in which a central concept is an egg. The system allows you to order eggs and see spending reports and inventory-centric data such as quantity on hand, usage, valuation and what have you. There area variety of services backing these behaviors. And say there is also another app which allows you to compose recipes that link to a particular egg type. Now egg type is broken down by the species—ostrich, goose, duck, chicken, quail. This is fine and dandy because it means that users don't end up with ostrich eggs when they wanted quail eggs and whatnot. However, we've been getting complaints because jumbo chicken eggs are not even close to equivalent to small ones. The price is different, and they really aren't substitutable in recipes. And here we thought we were doing users a favor by not overwhelming them with too many options. Currently each of the services (say, OrderSubmitter, EggTypeDefiner, SpendingReportsGenerator, InventoryTracker, RecipeCreator, RecipeTracker, or whatever) are identifying egg types with an industry-standard integer representation the species (let's call it speciesCode). We realize we've goofed up because this change could effect every service. There are two basic proposed solutions: Use a predefined identifier type like Guid as the eggTypeID throughout all the services, but make EggTypeDefiner the only service that knows that this maps to a speciesCode and eggSizeCode (and potentially to an isOrganic flag in the future, or whatever). Use an EggTypeID value object which is a combination of speciesCode and eggSizeCode in every service. I've proposed the first solution because I'm hoping it better encapsulates the definition of what an egg type is in the EggTypeDefiner and will be more resilient to changes, say if some people now want to differentiate eggs by whether or not they are "organic". The second solution is being suggested by some people who understand DDD better than I do in the hopes that less enrichment and lookup will be necessary that way, with the justification that in DDD using a value object as an ID is fine. Also, they are saying that EggTypeDefiner is not a domain and EggType is not an entity and as such should not have a Guid for an ID. However, I'm not sure the second solution is viable. This "value object" is going to have to be serialized into JSON and URLs for GET requests and used with a variety of technologies (C#, JavaScript...) which breaks encapsulation and thus removes any behavior of the identifier value object (is either of the fields optional? etc.) Is this a case where we want to avoid something that would normally be fine in DDD because we are trying to do DDD in a distributed fashion? Summary Can it be a good idea to use a custom value object as an identifier in a distributed system (solution #2)?

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  • DB Object passing between classes singleton, static or other?

    - by Stephen
    So I'm designing a reporting system at work it's my first project written OOP and I'm stuck on the design choice for the DB class. Obviously I only want to create one instance of the DB class per-session/user and then pass it to each of the classes that need it. What I don't know it what's best practice for implementing this. Currently I have code like the following:- class db { private $user = 'USER'; private $pass = 'PASS'; private $tables = array( 'user','report', 'etc...'); function __construct(){ //SET UP CONNECTION AND TABLES } }; class report{ function __construct ($params = array(), $db, $user) { //Error checking/handling trimed //$db is the database object we created $this->db = $db; //$this->user is the user object for the logged in user $this->user = $user; $this->reportCreate(); } public function setPermission($permissionId = 1) { //Note the $this->db is this the best practise solution? $this->db->permission->find($permissionId) //Note the $this->user is this the best practise solution? $this->user->checkPermission(1) $data=array(); $this->db->reportpermission->insert($data) } };//end report I've been reading about using static classes and have just come across Singletons (though these appear to be passé already?) so what's current best practice for doing this?

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  • Adding dynamic business logic/business process checks to a system

    - by Jordan Reiter
    I'm wondering if there is a good extant pattern (language here is Python/Django but also interested on the more abstract level) for creating a business logic layer that can be created without coding. For example, suppose that a house rental should only be available during a specific time. A coder might create the following class: from bizlogic import rules, LogicRule from orders.models import Order class BeachHouseAvailable(LogicRule): def check(self, reservation): house = reservation.house_reserved if not (house.earliest_available < reservation.starts < house.latest_available ) raise RuleViolationWhen("Beach house is available only between %s and %s" % (house.earliest_available, house.latest_available)) return True rules.add(Order, BeachHouseAvailable, name="BeachHouse Available") This is fine, but I don't want to have to code something like this each time a new rule is needed. I'd like to create something dynamic, ideally something that can be stored in a database. The thing is, it would have to be flexible enough to encompass a wide variety of rules: avoiding duplicates/overlaps (to continue the example "You already have a reservation for this time/location") logic rules ("You can't rent a house to yourself", "This house is in a different place from your chosen destination") sanity tests ("You've set a rental price that's 10x the normal rate. Are you sure this is the right price?" Things like that. Before I recreate the wheel, I'm wondering if there are already methods out there for doing something like this.

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  • Circular dependency and object creation when attempting DDD

    - by Matthew
    I have a domain where an Organization has People. Organization Entity public class Organization { private readonly List<Person> _people = new List<Person>(); public Person CreatePerson(string name) { var person = new Person(organization, name); _people.Add(person); return person; } public IEnumerable<Person> People { get { return _people; } } } Person Entity public class Person { public Person(Organization organization, string name) { if (organization == null) { throw new ArgumentNullException("organization"); } Organization = organization; Name = name; } public Organization { get; private set; } public Name { get; private set; } } The rule for this relationship is that a Person must belong to exactly one Organization. The invariants I want to guarantee are: A person must have an organization this is enforced via the Person's constuctor An organization must know of its people this is why the Organization has a CreatePerson method A person must belong to only one organization this is why the organization's people list is not publicly mutable (ignoring the casting to List, maybe ToEnumerable can enforce that, not too concerned about it though) What I want out of this is that if a person is created, that the organization knows about its creation. However, the problem with the model currently is that you are able to create a person without ever adding it to the organizations collection. Here's a failing unit-test to describe my problem [Test] public void AnOrganizationMustKnowOfItsPeople() { var organization = new Organization(); var person = new Person(organization, "Steve McQueen"); CollectionAssert.Contains(organization.People, person); } What is the most idiomatic way to enforce the invariants and the circular relationship?

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  • Ubiquitous Language and Custom types

    - by EdvRusj
    Note that my question is referring to those attributes that even on their own already represent a concept ( ie on their own provide a cohesive meaning ). Thus such attribute needs no additional functional support and as such is self-contained. I'm also well-aware that even with self-contained attributes the custom types may prove beneficial ( for example, they give the ability to add new behavior later, when business requirements change ). Thus, my question focuses only on whether custom types for self-contained attributes really enrich Ubiquitous Language UL a) I've read that in most cases, even simple, self-contained attributes should have custom, more descriptive types rather than basic value types ( double, string ... ), because among other things, descriptive types add to the UL, while the use of basic types instead weakens the language. I understand the importance of UL, but how does having a basic type for a self-contained attribute weaken the language, since with self-contained attributes the name of the attribute already adequately describes the concept and thus contributes to the UL vocabulary? For example, the term person_age already adequately explains the concept of quantifying the number of years a person has: class Person { string person_age; } so what could we possibly gain by also introducing the term ThingAge to the UL: class person { ThingAge person_age; } thanks

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