virtual

Multiple dispatch solution with full maintainability

由 一世执手 提交于 2019-11-27 06:32:52
问题 Can someone think of a good way to implement multiple dispatch with something like the Object::foo overloads below? class A { public: virtual void accept (Visitor&) = 0; }; class B : public A { virtual void accept (Visitor&) override; }; class C : public A { virtual void accept (Visitor&) override; }; class D : public A { virtual void accept (Visitor&) override; }; class Object { public: virtual double foo (A*, A*) { std::cout << "Object::foo A,A\n"; return 3.14; } virtual double foo (B*, B*)

Pagination sort link on a virtual field/entity property in CakePHP 3.0

由 本小妞迷上赌 提交于 2019-11-27 06:04:54
问题 I want to create a pagination sort link on a virtual field/entity property in CakePHP 3.0. In CakePHP 2.x I used to create a virtual field, and then create a pagination sort link on that field. However, in CakePHP 3.0, virtual fields have been replaced by virtual entity properties. Is there any way I can get this working in CakePHP 3.0? In my situation, I have a first_name and last_name column, which are combined as full_name in a virtual entity property. I want to sort on the full_name. 回答1:

Overload resolution of virtual methods

由 可紊 提交于 2019-11-27 06:04:07
问题 Consider the code public class Base { public virtual int Add(int a,int b) { return a+b; } } public class Derived:Base { public override int Add(int a,int b) { return a+b; } public int Add(float a,float b) { return (Int32)(a + b); } } If I create an instance of Derived class and call Add with parameters of type int why it is calling the Add method with float parameters Derived obj =new Derived() obj.Add(3,5) // why this is calling Add(float a,float b) Why it is not calling the more specific

The difference between virtual, override, new and sealed override

由 拥有回忆 提交于 2019-11-27 06:02:54
I'm pretty confused between some concepts of OOP: virtual , override , new and sealed override . Can anyone explain the differences? I am pretty clear that if the derived class method is to be used, one can use the override keyword so that the base class method will be overriden by derived class. But I'm not sure about new , and sealed override . CharithJ The virtual keyword is used to modify a method, property, indexer or event declaration, and allow it to be overridden in a derived class. For example, this method can be overridden by any class that inherits it: Use the new modifier to

Confused about “override” vs. “new” in C#

由 ℡╲_俬逩灬. 提交于 2019-11-27 05:48:36
问题 I'm having the following classes: class Base { public virtual void Print() { Console.WriteLine("Base"); } } class Der1 : Base { public new virtual void Print() { Console.WriteLine("Der1"); } } class Der2 : Der1 { public override void Print() { Console.WriteLine("Der2"); } } This is my main method: Base b = new Der2(); Der1 d1 = new Der2(); Der2 d2 = new Der2(); b.Print(); d1.Print(); d2.Print(); The output is Base , Der2 , Der2 . As far as I know, Override won't let previous method to run,

How does virtual method invocation work in C++?

由 |▌冷眼眸甩不掉的悲伤 提交于 2019-11-27 05:29:27
How does Virtual Method Invocation work in C++? Through virtual tables. Read this article, http://en.wikipedia.org/wiki/Virtual_table . I could explain it here, but the wikipedia does a better job than I could. The C++ standard doesn't specify how the virtual function mechanism should be implemented. That said, I think all current C++ compilers use virtual tables. The common way to do this for classes which contain at least one virtual function to have a hidden pointer to a so-called virtual table, where the addresses of the virtual functions for a specific class are entered in compiler

How to implement virtual static properties?

由 痞子三分冷 提交于 2019-11-27 05:27:22
As far as I know C# doesn't support virtual static properties. How to implement such a behavior in C# ? I want to archive that all derived classes of a base class must override a static property. Getting a derived type, I want to access to a static property called Identifier Type t = typeof(DerivedClass); var identifier= (String) t.GetProperty("Identifier", BindingFlags.Static).GetValue(null, null); For you still don't have an accpted answer about five years later, let me give it a try(again) .. I've ever thought about the Curiously Recurring Template Pattern as a workaround, but since you'll

Difference between target google APIs and target android

由 浪尽此生 提交于 2019-11-27 05:11:18
问题 I'm developing android with SDK 2.3.3 using Eclipse IDE. As you all know to run my app, I should generate virtual device. From 'create new AVD' window, I can see many targets. There are 2 targets for API level 10 such as 'android 2.3.3' and Google APIs(Google Inc). Among those targets, I'm uncertain which one I should choose. My question is what's the difference between them. Thanks in advance Dan 回答1: The Google API includes Google Maps and other Google-specific libraries. The Android one

How to make an array with polymorphism in C++? [duplicate]

由 不打扰是莪最后的温柔 提交于 2019-11-27 04:46:07
问题 This question already has answers here : Polymorphism & Pointers to arrays [duplicate] (3 answers) Closed 5 years ago . class Base1 { private: int testInput; public: Base1(); virtual int GetRow(void) = 0; }; Base1::Base1() { testInput = 0; } class table : public Base1 { private: int row; public: table(); virtual int GetRow(void); }; table::table() { //Contructor row = 5; } int table::GetRow() { return row; } int main () { Base1* pBase = new table[3]; pBase[0].GetRow(); pBase[1].GetRow(); /

C++ virtual function table memory cost

由 蹲街弑〆低调 提交于 2019-11-27 04:31:11
问题 Consider: class A { public: virtual void update() = 0; } class B : public A { public: void update() { /* stuff goes in here... */ } private: double a, b, c; } class C { // Same kind of thing as B, but with different update function/data members } I'm now doing: A * array = new A[1000]; array[0] = new B(); array[1] = new C(); //etc., etc. If i call sizeof(B) , the size returned is the size required by the 3 double members, plus some overhead required for the virtual function pointer table. Now
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