inheritance

问题 This question already has answers here : Python method name with double-underscore is overridden? (2 answers) Closed 5 years ago . I have two classes that loosely take the form below: class Foo: def __init__(self, foo): self.__foo = foo class Bar(Foo): def bar(self): print self.__foo When I try to invoke the bar method on an instance of Bar , it fails. b = Bar('foobar') b.bar() Result: Traceback (most recent call last): File "foobar.py", line 14, in <module> b.bar() File "foobar.py", line 10,

问题 I'm having a performance issue with a LINQ to SQL model that has a lot of inherited classes. I isolated the issue and it seems to be some sort of issue with LINQ to SQL generated code itself. I created a sample program using Northwind to flesh out the issue. It returns the first row of Customer in both scenarios. The database query is trivial and runs <1ms. In the 'small' scenario, it has 4 types, with one base Customer and three derived types using LINQ inheritance. The the "large" scenario,

问题 Let's say I have: #include <Windows.h> #include <iostream> #include <vector> std::vector<int> Base::m_intList; class Base { public: Base(); protected: static std::vector<int> m_intList; }; class Derived : Base { public: Derived(); protected: bool fWhatever; }; class MoreDerived : Derived { public: MoreDerived(); private: HRESULT DoStuff(); }; Base::Base() { } Derived::Derived() { } MoreDerived::MoreDerived() { } HRESULT MoreDerived::DoStuff() { for (auto it = m_intList.begin(); it != m

问题 Within my app, I have multiple UIView subclasses that depend on a model. Each of the classes adopting ' Restorable ' protocol which holds the superclass of the model. Each sub-model describes the specific UIView not-common properties. // Super-model public protocol StoryItem { var id: Int64? { get } } // Parent protocol public protocol Restorable: AnyObject { var storyItem: StoryItem? { get set } } // Specific protocol public struct TextItem: StoryItem { public var id: Int64? public var text:

问题 class A{ int a=10; public void show(){ System.out.println("Show A: "+a); } } class B extends A{ public int b=20; public void show(){ System.out.println("Show B: "+b); } } public class DynamicMethodDispatch { public static void main(String[] args) { A aObj = new A(); aObj.show(); //output - 10 B bObj = new B(); bObj.show(); //output - 20 aObj = bObj; //assigning the B obj to A.. aObj.show(); //output - 20 aObj = new B(); aObj.show(); //output - 20 System.out.println(bObj.b); //output - 20 /

问题 First something that should work, then something that doesn't. Why doesn't it is the question. I declare two classes: class Base { ... }; class Derived : public Base { ... }; I then have the following function elsewhere: void foo(shared_ptr<Base> base); The following code should work right? share_ptr<Derived> derived; foo(derived); Now, forget the above, I declare three classes: class Foo { ... }; template <typename TYPE> class Base { ... }; class Derived : public Base<Foo> { ... }; Elsewhere

问题 I have: Master object function Fruit() { this.type = "fruit"; } Sub-object: function Bannana() { this.color = "yellow"; } Inherit master properties Bannana.prototype = Object.create( Fruit.prototype ); var myBanana = new Bannana(); console.log( myBanana.type ); Outputs: undefined . Why is this not displaying "fruit" as the outcome? 回答1: Why is this not displaying "fruit" as the outcome? Because you are never setting type on the new object. type isn't a property of Fruit.prototype , and all

问题 SCENARIO I'm using a 3rd party windows visual theme. When I see my application, it looks like this: But when I use the normal Aero theme, it looks with horrible white borders everywhere: QUESTION I know that the color-scheme used in the app depends on the visual style, but: I can inherit the TextBox , ComboBox , and TabControl to change the drawn border color to use a darker color? How to? UPDATE My TextBoxes are using a BorderStyle property value of Fixed3D My ComboBoxes are using a

问题 Is there a difference between these two function declarations? func doSomething<T: UIViewController>(controller: T) {...} vs. func doSomething(controller: UIViewController) {...} In Type Constraint Syntax section of the Apples Swift programming language book, there's this code sample: func​ ​someFunction​<​T​: ​SomeClass​, ​U​: ​SomeProtocol​>(​someT​: ​T​, ​someU​: ​U​) { // function body goes here } with this description: The hypothetical function above has two type parameters. The first

问题 I was looking at this answer, and I don't understand the logic behind why methods would be polymorphic but not fields. All member functions are polymorphic in Java by default. That means when you call this.toString() Java uses dynamic binding to resolve the call, calling the child version. When you access the member x, you access the member of your current scope (the father) because members are not polymorphic. When you have some field x in both the super and subclass, and override toString