polymorphism

问题 Can anyone explain the actual use of method hiding in C# with a valid example ? If the method is defined using the new keyword in the derived class, then it cannot be overridden. Then it is the same as creating a fresh method (other than the one mentioned in the base class) with a different name. Is there any specific reason to use the new keyword? 回答1: C# not only supports method overriding, but also method hiding. Simply put, if a method is not overriding the derived method, it is hiding it

问题 I need to have a std::vector of boost::ptr_vector s. To make their management easier, I enclosed the boost::ptr_vector in a class ( Zoo ) and made a std::vector of it ( allZoos ). Look at a minimal code for reproducing this: #include <boost/ptr_container/ptr_vector.hpp> #include <boost/utility.hpp> class Animal { public: virtual char type() = 0; }; class Cat : public Animal { public: char type() { return 1; } }; class Zoo { public: boost::ptr_vector<Animal> animals; }; int main() { std:

问题 I'm trying to write a method of a class that should get an object (such as textbox or label) as a parameter and whenever it needs to show a message to the user it uses the object to show the message. As the class will be used in other programs, it should be a little portable and it should implement the functioning to any text-based object such as labels or textboxs etc. Consider the following method: public void TcpEndPoint(string IP,/* a text-based object */) { // There's a need to show a

问题 In my ASP.NET Core API, I have a DTO class BaseDto and another DerivedDto that inherits from BaseDto and hides some of its properties, because they're required in DerivedDto . I also have a BaseModel class to which both BaseDto and DerivedDto will be mapped through another class Mapper . Something like the following code: using System.ComponentModel.DataAnnotations; public class BaseDto { public string Name { get; set; } } public class DerivedDto : BaseDto { [Required] public new string Name

问题 Consider the following program #include <iostream> #include <iomanip> struct A { }; struct C { }; int main() { C *pc = nullptr; A *pa1 = dynamic_cast<A *>( pc ); std::cout << "pa1 == nullptr is " << std::boolalpha << ( pa1 == nullptr ) << '\n'; A *pa2 = pc; std::cout << "pa2 == nullptr is " << std::boolalpha << ( pa2 == nullptr ) << '\n'; } For the both pointer declarations, pa1 and pa2, the compiler reports an error that such an initialization is not allowed. For example the clang HEAD 10.0

问题 Interface: template <class T> class Interface{ public: typedef T Units; virtual T get() = 0; }; Implementation1: class Implementation1: public Interface<float> { public: float get() { return 0.0f; } }; Implementation2: class Implementation2: public Interface<int> { public: int get() { return 0; } }; Container (with errors): class Container{ private: Interface* floatGetter; int n; Timer::Units* array; public: Container(Interface* floatGetter, int n) { this->floatGetter= floatGetter; this->n =

问题 Basically, given {-# LANGUAGE PolymorphicKinds, ConstraintKinds, TypeFamilies #-} (and more, if necessary), does the (~) type-level operator work on type-level expressions of kind Constraint ? I tried googling the answer, but had no luck. 回答1: Yes, it is possible. Because types of kind Constraint are finite sets of atomic type constraints, you can test their equality very easily. The PolyKinds extension is not necessary, however. Also, there's very few situations when this kind equality would

问题 I guess I got stuck in thinking about a polymorphism solution to my following problem: Let's say I have a BaseTX struct with fields for a transaction. Now I have two special types of transactions: RewardTX struct and AllowanceTX struct . RewardTX struct has at this moment only the composition of BaseTX struct . AllowanceTX struct has a composition of BaseTX struct and an AddField . I have also a function logicAndSaveTX() , which has some logic on fields from BaseTX but at the end is

问题 I'm trying to expose my C++ Classes to Python using Boost.Python. Here is a simplyfied version of what I'm trying to do: struct Base { virtual ~Base() {}; virtual char const *Hello() { printf("Base.Hello\n"); return "Hello. I'm Base."; }; }; struct Derived : Base { char const *Hello() { printf("Derived.Hello\n"); return "Hello. I'm Derived."; }; Base &test() { printf("Derived.test\n"); // ... // After some calculation, we get result reference `instance' // `instance' can be an instance of

问题 I'm new to smart pointers and I would be really grateful if somebody could give me a hint whether the way I'm handling smart pointers as class members is correct. More precisely, the solution that I would like to achieve is in the context of class polymorphism and should be ideally exception-safe. Given a container of heterogeneuous objects ( std::vector<shared_ptr<CBase> > my_vector ), the usual way to add elements is: my_vector.push_back( shared_ptr<CBase>(new CChild(1))) , so that later on