inheritance

问题 I have a class that has to take a custom widget. This one can have two different implementations, so I would like to have an abstract class as interface and create two other classes those extend the abstract one. So, I have: abstract class ICustomWidget extends StatelessWidget{} class A extends ICustomWidget{ @override Widget build(BuildContext context) => //Implementation } class B extends ICustomWidget { @override Widget build(BuildContext context) => //Implementation } I want to ask if

问题 I have a class that has to take a custom widget. This one can have two different implementations, so I would like to have an abstract class as interface and create two other classes those extend the abstract one. So, I have: abstract class ICustomWidget extends StatelessWidget{} class A extends ICustomWidget{ @override Widget build(BuildContext context) => //Implementation } class B extends ICustomWidget { @override Widget build(BuildContext context) => //Implementation } I want to ask if

问题 I have a class that has to take a custom widget. This one can have two different implementations, so I would like to have an abstract class as interface and create two other classes those extend the abstract one. So, I have: abstract class ICustomWidget extends StatelessWidget{} class A extends ICustomWidget{ @override Widget build(BuildContext context) => //Implementation } class B extends ICustomWidget { @override Widget build(BuildContext context) => //Implementation } I want to ask if

问题 Is it mandatory to call the parent's constructor from the constructor in the child class constructor? To explain consider the following example: class Parent{ function __construct(){ //something is done here. } } class Child extends Parent{ function __construct(){ parent::__construct(); //do something here. } } This is quite normal to do it as above. But consider the following constructors of the class Child : function __construct(){ //Do something here parent::__construct(); } Is the above

问题 I understand mixin as what looks like inheritance but what is more like composition. (edit: I tend to think giving additional functionality/attributes by mixin rather than giving another is-a relationship .) Mentally, I'm saying something like this when I use mixin: I'm giving you this mixin you are missing, rather than you are actually this mixin-type as well.(is-a) And I read few times, you should prefer composition over inheritance. We could just use straight compositions instead of mixins

问题 I understand mixin as what looks like inheritance but what is more like composition. (edit: I tend to think giving additional functionality/attributes by mixin rather than giving another is-a relationship .) Mentally, I'm saying something like this when I use mixin: I'm giving you this mixin you are missing, rather than you are actually this mixin-type as well.(is-a) And I read few times, you should prefer composition over inheritance. We could just use straight compositions instead of mixins

问题 What does the : indicates in the class or interface definition in C#. public interface IServer : IServerManager, ISimulation, ISiteEx { /// <summary> /// Returns the highest game version that supported by this server. /// Higher versions aren't guaranteed to work perfect. /// </summary> Version MaxSupportedGameVersion { get; } /// <summary> /// Gets/sets the current server configuration. /// </summary> ServerConfiguration Configuration { get; set; } } 回答1: : is used to indicate that the

问题 I am not quite used to class inheritance in Python yet. All I want to do is simply pass all arguments from my base class to the super class when it is created: class A: def __init__(self, a, b): self.a = a self.b = b def do(self): c = self.a + self.b return B(c=c) class B(A): def __init__(self, c): self.c = c my_A = A(a=1, b=2) my_B = my_A.do() print(my_B.c) This works as expected. However, what I want is to also be able to call the arguments a and b from the x2 instance of the class my_B, so

问题 I have a simple R6 object generator: thing <- R6Class("youngThing", private = list( ..age = 0), active = list( age = function(){ private$..age <- private$..age + 1 private$..age } ) ) That gives me a simple R6 object, where ..age increases by 1 every time the active age field is called: a_thing <- thing$new() a_thing$age # [1] 1 I want the object class of a_thing to change given a threshold value of the private field ..age , like this: class(a_thing) # [1] "youngThing" "R6" for(timestep in 1

问题 I'm trying to access the member variable x in struct Top using a Bottom object. The code is the following: #include <cstdio> struct Top { public: int x = 1; }; struct Left : public Top { int x = 2; }; struct Right : public Top { int x = 3; }; struct Bottom : public Left, public Right { int x = 4; }; int main() { Bottom b; std::printf("value: %d\n", b.Left::Top::x); return 0; } This gives the following error using gcc 4.8: main.cpp: In function 'int main()': main.cpp:27:45: error: 'Top' is an