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  • C++ superclass constructor calling rules

    - by levik
    What are the C++ rules for calling the superclass constructor from a subclass one?? For example I know in Java, you must do it as the first line of the subclass constructor (and if you don't an implicit call to a no-arg super constructor is assumed - giving you a compile error if that's missing).

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  • Is it possible to override a property and return a derived type in VB.NET?

    - by Casey
    Consider the following classes representing an Ordering system: Public Class OrderBase Public MustOverride Property OrderItem() as OrderItemBase End Class Public Class OrderItemBase End Class Now, suppose we want to extend these classes to a more specific set of order classes, keeping the aggregate nature of OrderBase: Public Class WebOrder Inherits OrderBase Public Overrides Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class The Overriden property in the WebOrder class will cause an error stating that the return type is different from that defined in OrderBase... however, the return type is a subclass of the type defined in OrderBase. Why won't VB allow this?

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  • Doing things with objects as if they were parents

    - by General Ackbar
    Sorry that this is probably a super noob question. But the following code give me an error saying that there are invalid arguments in my call of doStuffToLines(segments) shouldnt I be able to do this since I have my DimensionLineSegment inherits from Lines? private void doStuff() { List<DimensionLineSegment> segments = new List<DimensionLineSegment>(); doStuffToLines(segments); } private void doStuffToLines(List<Line> lines) { }

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  • Inheritence and usage of dynamic_cast

    - by Mewzer
    Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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  • PHP: How to Pass child class __construct() arguments to parent::__construct() ?

    - by none
    I have a class in PHP like so: class ParentClass { function __construct($arg) { // Initialize a/some variable(s) based on $arg } } It has a child class, as such: class ChildClass extends ParentClass { function __construct($arg) { // Let the parent handle construction. parent::__construct($arg); } } What if, for some reason, the ParentClass needs to change to take more than one optional argument, which I would like my Child class to provide "just in case"? Unless I re-code the ChildClass, it will only ever take the one argument to the constructor, and will only ever pass that one argument. Is this so rare or such a bad practice that the usual case is that a ChildClass wouldn't need to be inheriting from a ParentClass that takes different arguments? Essentially, I've seen in Python where you can pass a potentially unknown number of arguments to a function via somefunction(*args) where 'args' is an array/iterable of some kind. Does something like this exist in PHP? Or should I refactor these classes before proceeding?

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  • (Cocoa) Can I Subclass and Delegate at the same time?

    - by Alvin
    @interface ClassB <ClassADelegate> : ClassA id <ClassBDelegate> delegate; @end As the code says, ClassB subclasses from ClassA and handles the formation protocol of Class A. However, the variable "delegate" will be duplicated. (ClassA also has "delegate") In fact, it can be done without subclassing, but it seems the code is cumbersome, i.e., to use a variable/function of ClassA, I need to write [[ClassB classA] doSomething] instead of [classB doSomething], where doSomething: is a function of ClassA. Are there any tidy way for me to do that?

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  • In Java, is it possible for a super constructor invocation actually invoke a constructor in the calling class?

    - by John Assymptoth
    Super constructor invocation definition: [Primary.] [NonWildTypeArguments] super ( ArgumentListopt ) ; A super constructor call can be prefixed by an Primary expression. Example (taken from JLS): class Outer { class Inner{ } } class ChildOfInner extends Outer.Inner { ChildOfInner() { (new Outer()).super(); // (new Outer()) is the Primary } } Does a Primary expression exist that makes the call to super() the invocation of a constructor of the calling class? Or Java prevents that?

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  • Java: using generic wildcards with subclassing

    - by gibberish
    Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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  • A general declaration for all inherited classes

    - by Soham
    Consider, there is a class called SuperClass from which, ClassA, ClassB, ClassC is derived. From each one of those derived Classes, there are further more two classes are derived each called ChildClassAA and ChildClassAB[AB stands for Bth Child class from the Ath Class.Lets not really pull our hair on this nomenclature]. Now, ideally, I want to declare a general type as a private member of another Class say IndependentClass which can be initialized during run time as either of the objects of type ClassAor ClassB or ClassC and even the derived classes like ClassAA or ClassAB. Is there a possible way to do it?

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  • Consequences in PHP of implementing an interface through two different routes?

    - by Daniel Bingham
    What are the consequences of implementing the same interface through two different routes in PHP, are there any? What I mean, is something like this: interface baseInterface {} abstract class baseClass implements baseInterface { } interface myInterface extends baseInterface {} class myClass extends baseClass implements myInterface {} In this case myClass implements baseInterface from two different parents - myInterface and baseClass. Are there any consequences to this? My instinct is that PHP should handle this fine, but I just want to make sure. What exactly does PHP do in this case? Does it just check to see that the necessary functions are implemented for the interface each time it discovers it and call it a day or does it do something more?

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  • How to override the attr_protected?

    - by KandadaBoggu
    I have STI implementation as follows: class Automobile < ActiveRecord::Base end class Car < Automobile end class Truck < Automobile end class User < ActiveRecord::Base has_many :automobiles accepts_nested_attributes_for :automobiles end I am creating a list of automobiles for a user. For each automobile, the UI sets the type field and the properties associated with the automobile.While form submission, the type field is ignored as it is a protected attribute. How do I work around this issue? Is there a declarative way to unprotect a protected attribute?

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  • Is it possible to specify a return type of "Derivative(of T)" for a MustOverride sub in VB.NET?

    - by Casey
    VB.NET 2008 .NET 3.5 I have two base classes that are MustInherit (partial). Let's call one class OrderBase and the other OrderItemBase. A specific type of order and order item would inherit from these classes. Let's call these WebOrder (inherits from OrderBase) and WebOrderItem (inherits from OrderItemBase). Now, in the grand scheme of things WebOrder is a composite class containing a WebOrderItem, like so: Public Class WebOrder Inherits OrderBase Public Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class In order to make sure any class that derives from OrderBase has the OrderItem property, I would like to do something like this in the OrderBase class: Public MustInherit Class OrderBase Public MustOverride Property OrderItem() as Derivative(Of OrderItemBase) End Class In other words, I want the derived class to be forced to contain a property that returns a derivative of OrderItemBase. Is this possible, or should I be using an entirely different approach?

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  • question about class derivation in c++?

    - by jack22
    hi, i want to know some things about class derivation in c++ so i have super class x and an inherited class y and i did this class x{ public:a; private:b; protected:c; } class y:public x{ public:d; } in this case how y can access a,b,and c and by how i mean(public,protected,private) the second case: class x{ public:a; private:b; protected:c; } class y:private x{ public:d; } the same question? the third case: class x{ public:a; private:b; protected:c; } class y:private x{ public:d; } again the same question? sorry i think i wrote too much bye

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  • Display: table-cell problems in chrome

    - by F21
    I have 3 divs that I would like to display as table cells: <div class="field"> <div class="row"> <label for="name">Subdomain</label> <input type="text" id="name" name="name"> <div class="subdomain-base ">test</div> </div> </div> This is the CSS that I am using: body{ font-size: 13px; } .field { width:450px; display: table; } .row { display: table-row; width: 100%; } .row > * { display: table-cell; border: 1px solid red; } label { width: 125px; height: 18px; } input { max-width: none; min-width: 0; overflow: auto; height: 18px; width: 100%; } .subdomain-base { height: 18px; width: 1px; } .subdomain-base { color: blue; font-size: 13px; } It works perfectly in Firefox 24: However, it has a height problem in Chrome 30 (latest): I have been trying all sorts of things to fix the problem with Chrome, but it seems like nothing works. Why is chrome getting that extra height? Jsfiddle: http://jsfiddle.net/ahLMH/

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  • How to save derived type (TPT) in Entity Framework?

    - by Peter Stegnar
    I have problems with saving derived type (TPT) with Entity Framework to database. Let's say I have base entity Animal and derived type Dog. I want to save Dog entity. I thought that I could do it like contex.AddToDogs(), but contex contain only base entity - Animal. So I can only save Animal object - contex.AddToAnimals(). I have also tried with contex.AddObject("Animals", dogInstance), but I get the following error: The member with identity 'NavigationProperty' does not exist in the metadata collection. But I have add EntityReference to the "NavigationProperty". So how to save derived type in EF?

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  • django access to parent

    - by SledgehammerPL
    model: class Product(models.Model): name = models.CharField(max_length = 128) (...) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive And now I'd like to get list of the most often useable products: ReceiptComponent.objects.values('product').annotate(Count('product')).order_by('-product__count' the example result: [{'product': 3, 'product__count': 5}, {'product': 6, 'product__count': 4}, {'product': 5, 'product__count': 3}, {'product': 7, 'product__count': 2}, {'product': 1, 'product__count': 2}, {'product': 11, 'product__count': 1}, {'product': 8, 'product__count': 1}, {'product': 4, 'product__count': 1}, {'product': 9, 'product__count': 1}] It's almost what I need. But I'd prefer having Product object not product value, because I'd like to use this in views.py for generating list.

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  • Compile time type determination in C++

    - by dicroce
    A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an "is a" relationship with another type. I think this is totally awesome, but I have to admit that I'm clueless as to how this actually works. Can anyone explain this to me? template<typename BaseT, typename DerivedT> inline bool isRelated(const DerivedT&) { DerivedT derived(); char test(const BaseT&); // sizeof(test()) == sizeof(char) char (&test(...))[2]; // sizeof(test()) == sizeof(char[2]) struct conversion { enum { exists = (sizeof(test(derived())) == sizeof(char)) }; }; return conversion::exists; } Once this function is defined, you can use it like this: #include <iostream> class base {}; class derived : public base {}; class unrelated {}; int main() { base b; derived d; unrelated u; if( isRelated<base>( b ) ) std::cout << "b is related to base" << std::endl; if( isRelated<base>( d ) ) std::cout << "d is related to base" << std::endl; if( !isRelated<base>( u ) ) std::cout << "u is not related to base" << std::endl; }

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  • Javascript inherance and use of super: is this possible?

    - by Totty
    var Parent = function(value){ this.value = value; this.value1 = 3; this.hello = function(text){ alert(this.value1 + text); } } var Child = extends(Parent, function(value){ this.value1 = 1; this.hello = function(text){ this.super.hello(text); alert('Child' + this.value1 + this.value); } }) var child = new Child(2); child.hello('ola'); // this must output 2 alerts: // 1: "1ola" // 2: "Child1ola"

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  • HTML table cells not properly aligned

    - by Yuval A
    I have the following HTML table: <table style="width: 100%;"> <tr> <td class="title_bar_left_border"></td> <td class="title_bar_middle"></td> <td class="title_bar_right_border"></td> </tr> </table> With the following css rules: .title_bar_left_border { BACKGROUND-IMAGE: url(tray_left.gif); WIDTH: 3px; HEIGHT: 24px; } .title_bar_right_border { BACKGROUND-IMAGE: url(tray_right.gif); WIDTH: 3px; HEIGHT: 24px; } .title_bar_middle { BACKGROUND-IMAGE: url(tray_middle.gif); WIDTH: 100%; BACKGROUND-REPEAT: repeat-x; HEIGHT: 24px; } Any idea why this is the result? Instead of getting a nice table header with rounded corners you get this weird gap between the cells. Where are the gaps coming from? Besides fixing this ugly issue, I would like to understand the rationale as to why all browsers render the HTML this way.

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  • CSS: 100% of container height without modifying the container

    - by Rena
    Yeah, this ugly question again. I'm writing some HTML that gets inserted into a page. I have no control over the rest of the page. The structure is something like: <table <tr <td rowspan="2"left column</td <td height="1"top row above content</td </tr <tr<td height="220"my content here</td</tr </table I can write whatever I want into that table cell (including style tags to pack in my CSS), but I can't touch anything outside of it, which means I can't set the height of any parent element (including html and body), add a doctype (it has none), etc - that already kills just about every solution I can find (all seem to be "add a doctype" and/or "give the parent container a fixed height"). What I want to do is simply have a <div fill the entire cell. Width is no problem but unsurprisingly height is being a massive pain. Writing "height: 100%" doesn't do anything unless the container has a fixed height (the height="220" attribute apparently doesn't count) or the div uses absolute positioning - and then it seems to want to use 100% of the window's height (and width even) instead of the cell's. The root of the problem is the left column varies in height, as does the content, and when the left column cell is larger than the content, it won't expand to fill the cell it's in. If I set a fixed height for the content, it'll be much larger than necessary most of the time, and if I don't, it doesn't take up all of the cell and leaves an ugly gap at the bottom.

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  • How to change position of inherited items in an Inherited user control

    - by Yalda
    I have used a user control as a base class (let's call it BaseUC) with 3 labels (in 3 lines) on it (they are set as protected). And there is another user control that inherits from it (InheritedUC). I have added two more labels in InheritedUC, which are positioned between the base's labels (so there are 5 lines). Everything is fine is Visiual Studio's design UI view. But when I run the application, labels on BaseUC overlap with the ones in InheritedUC and I can't see the ones on the inherited control. Any ideas to fix this? Thank you very much

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