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  • concrete uses of LDAP?

    - by ajsie
    im new to LDAP. i wonder what are some concrete examples of using LDAP. things that are MUCH more easier to do when you got 3-7 linux computers in a small company network. one use that is very important for me seems to be that you configure LDAP to handle system authentication. then you dont have to create same accounts in all computers. are there other things that are a MUST DO for a small network to save more time? my small network is for apache servers and database servers. and should LDAP be in an own machine? cause i guess its not good to put it in apache or database servers since these are performance dependent.

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  • How to implement table-per-concrete-type strategy using entity framework

    - by SDReyes
    Hello Guys! I'm mapping a set of tables that share a common set of fields: So as you can see I'm using a table-per-concrete-type strategy to map the inheritance. But... I have not could to relate them to an abstract type containing these common properties. It's possible to do it using EF? BONUS: The only non documented Entity Data Model Mapping Scenario is Table-per-concrete-type inheritance http://msdn.microsoft.com/en-us/library/cc716779.aspx : P

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  • Multiple Inheritance Debates II: according to Stroutroup

    - by asksuperuser
    I know very well about the traditional arguments about why Interface Inheritance is prefered to multiple inheritance, there has been already a post here : http://stackoverflow.com/questions/191691/should-c-include-multiple-inheritance But according to Stroutroup the real reason why Microsoft and Sun decided to get rid off multiple inheritance is that they have vested interest to do so: instead of putting features in the languages, they put in frameworks so that people then become tied to their platform instead of people having the same capability at a language standard level. What do you think ?

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  • How to implement table-per-concrete-type using entity framework

    - by SDReyes
    Hello Guys! I'm mapping a set of tables that share a common set of fields: So as you can see I'm using a table-per-concrete-type strategy to map the inheritance. But... I have not could to relate them to an abstract type containing these common properties. It's possible to do it using EF? BONUS: The only non documented Entity Data Model Mapping Scenario is Table-per-concrete-type inheritance http://msdn.microsoft.com/en-us/library/cc716779.aspx : P

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  • Abstract class + Inheritance vs Interface

    - by RealityDysfunction
    Hello fellow programmers, I am reading a book on C# and the author is comparing Abstract classes and Interfaces. He claims that if you have the following "abstract class:" abstract class CloneableType { public abstract object Clone(); } Then you cannot do this: public class MiniVan : Car, CloneableType {} This, I understand. However he claims that because of this inability to do multiple inheritance that you should use an interface for CloneableType, like so: public interface ICloneable { object Clone(); } My question is, isn't this somewhat misleading, because you can create an abstract class which is "above" class Car with the method Clone, then have Car inherit that class and then Minivan will inherit Car with all these methods, CloneAble class - Car class - Minivan Class. What do you think? Thanks.

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  • Visitor-pattern vs inheritance for rendering

    - by akaltar
    I have a game engine that currently uses inheritance to provide a generic interface to do rendering: class renderable { public: void render(); }; Each class calls the gl_* functions itself, this makes the code hard to optimize and hard to implement something like setting the quality of rendering: class sphere : public renderable { public: void render() { glDrawElements(...); } }; I was thinking about implementing a system where I would create a Renderer class that would render my objects: class sphere { void render( renderer* r ) { r->renderme( *this ); } }; class renderer { renderme( sphere& sphere ) { // magically get render resources here // magically render a sphere here } }; My main problem is where should I store the VBOs and where should I Create them when using this method? Should I even use this approach or stick to the current one, perhaps something else? PS: I already asked this question on SO but got no proper answers.

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  • Inheritance of list-style-type property in Firefox (bug in Firebug?)

    - by Marcel Korpel
    Let's have a look at some comments on a page generated by Wordpress (it's not a site I maintain, I'm just wondering what's going on here). As these pages might disappear in the near future, I've put some screenshots online. Here's what I saw: Obviously, the list-item markers shouldn't be there. So I decided to look at the source using Firebug. As you can see, Firebug claims that the list-style property (containing none) is inherited from ol.commentlist. But if that's the case, why are the circle and the square visible? When checking the computed style, Firebug shows the list-style-types correctly. What's the correct behaviour? I just did a quick check in Chromium, whose Web Inspector gave a better view of reality (the list item markers were also displayed in this browser): According to WebKit, list-style of ol.commentlist isn't inherited, only the default value of list-style-type from the rendering engine. So, we may conclude that the output of both browsers is correct and that Firefox (Firebug) shows an incorrect representation of inherited styles. What does the CSS specification say? Inheritance will transfer the list-style values from OL and UL elements to LI elements. This is the recommended way to specify list style information. Not much about the inheritance of ol properties to uls. Is Firebug wrong in this respect? BTW, I managed to let the markers disappear by just changing line 312 of style.css to ol.commentlist, li.commentlist, ul.children { When also explicitly defining the list-style of ul.children to none, the markers are not painted. You can have a look at screenshots of Firebug and WebKit's Web Inspector in this case, if you like.

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  • Objective C - creating concrete class instances from base class depending upon type

    - by indiantroy
    Just to give a real world example, say the base class is Vehicle and concrete classes are TwoWheeler and FourWheeler. Now the type of the vehicle - TwoWheeler or FourWheeler, is decided by the base class Vehicle. When I create an instance of TwoWheeler/FourWheeler using alloc-init method, it calls the super implementation like below to set the value of common properties defined in the Vehicle class and out of these properties one of them is type that actually decides if the type is TwoWheeler or FourWheeler. if (self = [super initWithDictionary:dict]){ [self setOtherAttributes:dict]; return self; } Now when I get a collection of vehicles some of them could be TwoWheeler and others will be FourWheeler. Hence I cannot directly create an instance of TwoWheeler or FourWheeler like this Vehicle *v = [[TwoWheeler alloc] initWithDictionary:dict]; Is there any way I can create an instance of base class and once I know the type, create an instance of child class depending upon type and return it. With the current implementation, it would result in infinite loop because I call super implementation from concrete class. What would be the perfect design to handle this scenario when I don't know which concrete class should be instantiated beforehand?

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  • Inheritance, commands and event sourcing

    - by Arthis
    In order not to redo things several times I wanted to factorize common stuff. For Instance, let's say we have a cow and a horse. The cow produces milk, the horse runs fast, but both eat grass. public class Herbivorous { public void EatGrass(int quantity) { var evt= Build.GrassEaten .WithQuantity(quantity); RaiseEvent(evt); } } public class Horse : Herbivorous { public void RunFast() { var evt= Build.FastRun; RaiseEvent(evt); } } public class Cow: Herbivorous { public void ProduceMilk() { var evt= Build.MilkProduced; RaiseEvent(evt); } } To eat Grass, the command handler should be : public class EatGrassHandler : CommandHandler<EatGrass> { public override CommandValidation Execute(EatGrass cmd) { Contract.Requires<ArgumentNullException>(cmd != null); var herbivorous= EventRepository.GetById<Herbivorous>(cmd.Id); if (herbivorous.IsNull()) throw new AggregateRootInstanceNotFoundException(); herbivorous.EatGrass(cmd.Quantity); EventRepository.Save(herbivorous, cmd.CommitId); } } so far so good. I get a Herbivorous object , I have access to its EatGrass function, whether it is a horse or a cow doesn't matter really. The only problem is here : EventRepository.GetById<Herbivorous>(cmd.Id) Indeed, let's imagine we have a cow that has produced milk during the morning and now wants to eat grass. The EventRepository contains an event MilkProduced, and then come the command EatGrass. With the CommandHandler, we are no longer in the presence of a cow and the herbivorious doesn't know anything about producing milk . what should it do? Ignore the event and continue , thus allowing the inheritance and "general" commands? or throw an exception to forbid execution, it would mean only CowEatGrass, and HorseEatGrass might exists as commands ? Thanks for your help, I am just beginning with these kinds of problem, and I would be glad to have some news from someone more experienced.

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  • Code contracts and inheritance

    - by DigiMortal
    In my last posting about code contracts I introduced you how to force code contracts to classes through interfaces. In this posting I will go step further and I will show you how code contracts work in the case of inherited classes. As a first thing let’s take a look at my interface and code contracts. [ContractClass(typeof(ProductContracts))] public interface IProduct {     int Id { get; set; }     string Name { get; set; }     decimal Weight { get; set; }     decimal Price { get; set; } }   [ContractClassFor(typeof(IProduct))] internal sealed class ProductContracts : IProduct {     private ProductContracts() { }       int IProduct.Id     {         get         {             return default(int);         }         set         {             Contract.Requires(value > 0);         }     }       string IProduct.Name     {         get         {             return default(string);         }         set         {             Contract.Requires(!string.IsNullOrWhiteSpace(value));             Contract.Requires(value.Length <= 25);         }     }       decimal IProduct.Weight     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 3);             Contract.Requires(value < 100);         }     }       decimal IProduct.Price     {         get         {             return default(decimal);         }         set         {             Contract.Requires(value > 0);             Contract.Requires(value < 100);         }     } } And here is the product class that inherits IProduct interface. public class Product : IProduct {     public int Id { get; set; }     public string Name { get; set; }     public virtual decimal Weight { get; set; }     public decimal Price { get; set; } } if we run this code and violate the code contract set to Id we will get ContractException. public class Program {     static void Main(string[] args)     {         var product = new Product();         product.Id = -100;     } }   Now let’s make Product to be abstract class and let’s define new class called Food that adds one more contract to Weight property. public class Food : Product {     public override decimal Weight     {         get         {             return base.Weight;         }         set         {             Contract.Requires(value > 1);             Contract.Requires(value < 10);               base.Weight = value;         }     } } Now we should have the following rules at place for Food: weight must be greater than 1, weight must be greater than 3, weight must be less than 100, weight must be less than 10. Interesting part is what happens when we try to violate the lower and upper limits of Food weight. To see what happens let’s try to violate rules #2 and #4. Just comment one of the last lines out in the following method to test another assignment. public class Program {     static void Main(string[] args)     {         var food = new Food();         food.Weight = 12;         food.Weight = 2;     } } And here are the results as pictures to see where exceptions are thrown. Click on images to see them at original size. Violation of lower limit. Violation of upper limit. As you can see for both violations we get ContractException like expected. Code contracts inheritance is powerful and at same time dangerous feature. Although you can always narrow down the conditions that come from more general classes it is possible to define impossible or conflicting contracts at different points in inheritance hierarchy.

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  • Inheritance vs containment while extending a large legacy project

    - by Flot2011
    I have got a legacy Java project with a lot of code. The code uses MVC pattern and is well structured and well written. It also has a lot of unit tests and it is still actively maintained (bug fixing, minor features adding). Therefore I want to preserve the original structure and code style as much as possible. The new feature I am going to add is a conceptual one, so I have to make my changes all over the code. In order to minimize changes I decided not to extend existing classes but to use containment: class ExistingClass { // .... existing code // my code adding new functionality private ExistingClassExtension extension = new ExistingClassExtension(); public ExistingClassExtension getExtension() {return extension;} } ... // somewhere in code ExistingClass instance = new ExistingClass(); ... // when I need a new functionality instance.getExtension().newMethod1(); All functionality that I am adding is inside a new ExistingClassExtension class. Actually I am adding only these 2 lines to each class that needs to be extended. By doing so I also do not need to instantiate new, extended classes all over the code and I may use existing tests to make sure there is no regression. However my colleagues argue that in this situation doing so isn't a proper OOP approach, and I need to inherit from ExistingClass in order to add a new functionality. What do you think? I am aware of numerous inheritance/containment questions here, but I think my question is different.

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  • Modeling a cellphone bill: should I use single-table inheritance or polymorphic associations?

    - by Horace Loeb
    In my domain: Users have many Bills Bills have many BillItems (and therefore Users have many BillItems through Bills) Every BillItem is one of: Call SMS (text message) MMS (multimedia message) Data Here are the properties of each individual BillItem (some are common): My question is whether I should model this arrangement with single-table inheritance (i.e., one "bill_items" table with a "type" column) or polymorphism (separate tables for each BillItem type), and why.

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  • Who calls the Destructor of the class when operator delete is used in multiple inheritance.

    - by dicaprio-leonard
    This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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  • JavaScript objects and Crockford's The Good Parts

    - by Jonathan
    I've been thinking quite a bit about how to do OOP in JS, especially when it comes to encapsulation and inheritance, recently. According to Crockford, classical is harmful because of new(), and both prototypal and classical are limited because their use of constructor.prototype means you can't use closures for encapsulation. Recently, I've considered the following couple of points about encapsulation: Encapsulation kills performance. It makes you add functions to EACH member object rather than to the prototype, because each object's methods have different closures (each object has different private members). Encapsulation forces the ugly "var that = this" workaround, to get private helper functions to have access to the instance they're attached to. Either that or make sure you call them with privateFunction.apply(this) everytime. Are there workarounds for either of two issues I mentioned? if not, do you still consider encapsulation to be worth it? Sidenote: The functional pattern Crockford describes doesn't even let you add public methods that only touch public members, since it completely forgoes the use of new() and constructor.prototype. Wouldn't a hybrid approach where you use classical inheritance and new(), but also call Super.apply(this, arguments) to initialize private members and privileged methods, be superior?

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  • Augmenting functionality of subclasses without code duplication in C++

    - by Rob W
    I have to add common functionality to some classes that share the same superclass, preferably without bloating the superclass. The simplified inheritance chain looks like this: Element -> HTMLElement -> HTMLAnchorElement Element -> SVGElement -> SVGAlement The default doSomething() method on Element is no-op by default, but there are some subclasses that need an actual implementation that requires some extra overridden methods and instance members. I cannot put a full implementation of doSomething() in Element because 1) it is only relevant for some of the subclasses, 2) its implementation has a performance impact and 3) it depends on a method that could be overridden by a class in the inheritance chain between the superclass and a subclass, e.g. SVGElement in my example. Especially because of the third point, I wanted to solve the problem using a template class, as follows (it is a kind of decorator for classes): struct Element { virtual void doSomething() {} }; // T should be an instance of Element template<class T> struct AugmentedElement : public T { // doSomething is expensive and uses T virtual void doSomething() override {} // Used by doSomething virtual bool shouldDoSomething() = 0; }; class SVGElement : public Element { /* ... */ }; class SVGAElement : public AugmentedElement<SVGElement> { // some non-trivial check bool shouldDoSomething() { /* ... */ return true; } }; // Similarly for HTMLAElement and others I looked around (in the existing (huge) codebase and on the internet), but didn't find any similar code snippets, let alone an evaluation of the effectiveness and pitfalls of this approach. Is my design the right way to go, or is there a better way to add common functionality to some subclasses of a given superclass?

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  • Using Unity and interfaces, how do I create a concrete class that implements IDisposable

    - by Ryan ONeill
    I have an interface (IDbAccess) for a database access class so that I can unit test it using Unity. It all works fine in Unity and now I want to make the concrete database class implement IDisposable so that it closes the db connections. My problem is that Unity does not understand that my concrete class is disposable because the interface (IDbAccess) cannot implement another interface. So how can I write code like this (pseudo code) so that Unity is aware that it needs to dispose the class as soon as I am done? Using var MyDbAccessInstance = Unity.Resolve<IDbAccess> { } Thanks Ryan

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  • Concrete Implementation of Generic Form Not Working in Designer

    - by Dov
    I have a base class, defined as below (I'm also using DevExpress components): public abstract partial class BaseFormClass<R> : XtraForm where R : DataRow { ... } Contrary to what I've read from elsewhere, I'm still able to design this class. I didn't have to create a concrete class from it to do so. But, when I create a concrete class descended from it (as below), that class won't work in the designer. public partial class ConcreteFormClass : BaseFormClass<StronglyTypedRow> { ... } I get this message: The designer could not be shown for this file because none of the classes within it can be designed. The designer inspected the following classes in the file: ConcreteFormClass --- The base class 'BaseFormClass' could not be loaded. Ensure the assembly has been referenced and that all projects have been built. Has anyone seen this before? Any sort of known workaround?

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  • Is there a practical alternative to struct inheritance? (C#)

    - by Tim Coulter
    I am writing code that will populate the Margin, Padding and BorderThickness properties of classes in the System.Windows.Documents namespace. Each of these properties accepts a value in the form of a System.Windows.Thickness, which is a struct. However, I wish to associate some additional data with each of these property assignments, which may subsequently be retrieved by my code. If Thickness were a class, I would inherit from it and define properties in the subclass to store my additional data items. But since it is a struct, inheritance is not possible. Is there any practical way to achieve this, while maintaining type-compatibility with the properties I am populating? Thanks for your ideas, Tim

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  • for a single-table inheritance in rails, how do I know the 'type' when creating a record?

    - by Angela
    I have several models which are very similar: Contact_Emails, Contact_Letters, Contact_Calls -- and I think life could be easier making them into a Single Table Inheritance called Contact_Event. However, the way I have it set up now is when something is created for a Contact_Email, I have a dedicated controller that I call and know that I am passing the arguments that are approrpriate. For example, new_contact_email(contact, email). I then have: Emails.find(email.contact_id), etcera, all very specific to that Model. I'm not sure how I extract the class/models to use. For example, I currently have the following because I have separate controllers for each model: def do_event(contact, call_or_email_or_letter) model_name = call_or_email_or_letter.class.name.tableize.singularize link_to( "#{model_name.camelize}", send("new_contact_#{model_name}_path", :contact => contact, :status => 'done', :"#{model_name}" => call_or_email_or_letter ) ) end What I really want is to: link_to("#model_name.camelize}", send("new_contact_event_path(contact,call_or_email_or_letter)"

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  • How do I create the Controller for a Single Table Inheritance in Rails?

    - by Angela
    I am setting up the Single Table Inheritance, using ContactEvent as the Model that ContactEmail, ContactLetter, and ContactCall will all inherit. But I'm stumped on how to create the routing and the controller. For example, let's say I want to create a new ContactEvent with type Email. I would like a way to do the following: new_contact_event_path(contact, email) This would take the instance from Contact model and from Email model. Inside, I would imagine the contact_event_controller would need to know... @contact_event.type = (params[:email]) # get the type based on what was passed in? @contact_event.event_id = (params[:email]) #get the id for the correct class, in this case Email.id Just not sure how this works....

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