inheritance

问题 Assuming I have a base class A and publicly derived class B, how should I assign A object to the A base class subobject of B? class A {...}; class B : public A {...}; A a(..); B b(..); static_cast<A&>(b) = a; ??? Is that doable without writing assignement operator for B? Are there any potential problems with casting b to A&? Is that standard conformant? 回答1: Writing another answer to demonstrate why and how assign a base class object to a derived class object. struct TimeMachineThing_Data { .

问题 I have this ModelForm: class Event(forms.ModelForm): def __init__(self, *args, **kwargs): super(Event, self).__init__(*args, **kwargs) ##Here make some changes such as: self.helper = FormHelper() self.helper.form_method = 'POST' ##Many settings here which **i don't want to rewrite in 10 child classes** class Meta: model = Event exclude = something... widgets = some settings here also. And this child ModelForm: class UpgradedEvent(Event): def __init__(self, *args, **kwargs): super

问题 I have this ModelForm: class Event(forms.ModelForm): def __init__(self, *args, **kwargs): super(Event, self).__init__(*args, **kwargs) ##Here make some changes such as: self.helper = FormHelper() self.helper.form_method = 'POST' ##Many settings here which **i don't want to rewrite in 10 child classes** class Meta: model = Event exclude = something... widgets = some settings here also. And this child ModelForm: class UpgradedEvent(Event): def __init__(self, *args, **kwargs): super

问题 In C++ since private inheritance is not considered as an is-a relationship, how is it supposed to be shown in a class diagram and if it is shown as a has-a relationship then how can it be differentiated between a composition and a private inheritance? 回答1: It should be a Composition relationship (solid black diamond on the subclass side), because: Private inheritance means "implemented in terms of" but in this regard it can be simply treated the same as "has a" relationship. An instance of

问题 Sean Parent's talk, Inheritance is the base class of evil, says that polymorphism is not a property of the type, but rather a property of how it is used. As a thumb rule, don't use inheritance to implement interfaces. Among the many benefits of this is the devirtualization of classes which have virtual functions only because they were implementing an interface. Here's an example : class Drawable { public: virtual void draw() = 0; }; class DrawA : public Drawable { public: void draw() override

问题 I think I understand the concept of "name mangling" in python, but there's something that I probably missed. Take a look at the following code: #!/usr/bin/env python class Base(object): __data = "Base" @classmethod def func(cls): return "Class name is {}, data is {}".format(cls.__name__, cls.__data) class A(Base): __data = "A" class B(A): __data = "B" print Base.func() print A.func() print B.func() Here the output I get: Class name is Base, data is Base Class name is A, data is Base Class

问题 I think I understand the concept of "name mangling" in python, but there's something that I probably missed. Take a look at the following code: #!/usr/bin/env python class Base(object): __data = "Base" @classmethod def func(cls): return "Class name is {}, data is {}".format(cls.__name__, cls.__data) class A(Base): __data = "A" class B(A): __data = "B" print Base.func() print A.func() print B.func() Here the output I get: Class name is Base, data is Base Class name is A, data is Base Class

问题 I think I understand the concept of "name mangling" in python, but there's something that I probably missed. Take a look at the following code: #!/usr/bin/env python class Base(object): __data = "Base" @classmethod def func(cls): return "Class name is {}, data is {}".format(cls.__name__, cls.__data) class A(Base): __data = "A" class B(A): __data = "B" print Base.func() print A.func() print B.func() Here the output I get: Class name is Base, data is Base Class name is A, data is Base Class

问题 I think I understand the concept of "name mangling" in python, but there's something that I probably missed. Take a look at the following code: #!/usr/bin/env python class Base(object): __data = "Base" @classmethod def func(cls): return "Class name is {}, data is {}".format(cls.__name__, cls.__data) class A(Base): __data = "A" class B(A): __data = "B" print Base.func() print A.func() print B.func() Here the output I get: Class name is Base, data is Base Class name is A, data is Base Class

问题 I'm having a bit of trouble figuring out this error I have. So I have a Person class, and a Student subclass. The Person class has the following constructor: Person(const string &name) { this->name = name; } The Student class has the following constructor: Student::Student(const string &name, int regNo) { this->name = name; this->regNo = regNo; } When I try to compile the Student class though, I get this error for the constructor: In constructor 'Student::Student(const string&, int)': error: