inheritance

问题 Given the following example: class ProfileTab: Identifiable { let id = UUID() let name: String init(name: String) { self.name = name } } class ProfileQuoteTab: ProfileTab { let answer: String let prompt: String init(name: String, answer: String, prompt: String) { self.answer = answer self.prompt = prompt super.init(name: name) } } class ProfileImageTab: ProfileTab { let image: Image init(name: String, image: Image) { self.image = image super.init(name: name) } } struct ContentView: View { let

问题 Here is the problem: I keep getting the unimplemented pure virtual method error when trying to compile. I have implemented all of the pure virtual methods in the abstract base class. Any ideas? here is the abstract base class: class record{ public: virtual int getID()=0; virtual record *clone(); }; and the implementation: class sdata: public record{ public: sdata(std::string s = ""){data=s; ID=atoi(data.substr(0,8).c_str());} virtual int getID(){return ID;} private: std::string data; int ID;

问题 Here is the problem: I keep getting the unimplemented pure virtual method error when trying to compile. I have implemented all of the pure virtual methods in the abstract base class. Any ideas? here is the abstract base class: class record{ public: virtual int getID()=0; virtual record *clone(); }; and the implementation: class sdata: public record{ public: sdata(std::string s = ""){data=s; ID=atoi(data.substr(0,8).c_str());} virtual int getID(){return ID;} private: std::string data; int ID;

问题 Is it wrong to have a lot of parameters inside a constructor? Like 10 to 15 parameters? Because I was designing a class where a constructor will have lots of parameters, for example, a Person class. My example person class has 6 parameters in its constructor: public class Person { private String fName; private String lName; private String mInitial; private int age; private String contactNumber; private String emailAddress; public Person(String fName, String lName, String mInitial, int age,

问题 I am facing some inconsistency in calling toString method for case-classes in Scala. The first code sample: case class Person(name: String, age: Int) val jim = Person("jim", 42) println(jim) output: Person(jim,42) For the next code sample I used a case class that extends Exception : case class JimOverslept(msg: String) extends Exception try { throw JimOverslept(msg = "went to bed late") } catch { case e: JimOverslept => println(e) } output: playground.CaseClassOutput$JimOverslept Actually, I

问题 I am facing some inconsistency in calling toString method for case-classes in Scala. The first code sample: case class Person(name: String, age: Int) val jim = Person("jim", 42) println(jim) output: Person(jim,42) For the next code sample I used a case class that extends Exception : case class JimOverslept(msg: String) extends Exception try { throw JimOverslept(msg = "went to bed late") } catch { case e: JimOverslept => println(e) } output: playground.CaseClassOutput$JimOverslept Actually, I

问题 I am facing some inconsistency in calling toString method for case-classes in Scala. The first code sample: case class Person(name: String, age: Int) val jim = Person("jim", 42) println(jim) output: Person(jim,42) For the next code sample I used a case class that extends Exception : case class JimOverslept(msg: String) extends Exception try { throw JimOverslept(msg = "went to bed late") } catch { case e: JimOverslept => println(e) } output: playground.CaseClassOutput$JimOverslept Actually, I

问题 I'm using inheritance and I ended up having a problem. If I run: select count(*) from estate_properties where id = 86820; I get 1. But when I try to run this: insert into property_images (binary_image, name, property_id) values (16779, 'IMG_0096.jpg', 86820) I get: ********** Error ********** ERROR: insert or update on table "property_images" violates foreign key constraint "property_images_property_id_fkey" SQL state: 23503 Detail: Key (property_id)=(86820) is not present in table "estate

问题 The following code compiles successfully without any compilation errors but how can we create Array(object) for Interface using new Keyword with the interface name. Objects can be created for the implementing class and can be referred by the interface like interface MyInterface{} class MyClass1 implements MyInterface{} class MyClass2 implements MyInterface{} class Test{ MyInterface[] interfaceArray=new MyClass1[7]; //Valid reason } Now the other case is creating object for the Interface

问题 I managed to reproduce this on both Python 3.4 and 3.7. Consider: class Comparable: def _key(self): raise NotImplementedError def __hash__(self): return hash(self._key()) def __eq__(self, other): ... def __lt__(self, other): ... class A(Comparable): pass class B(A): def __str__(self): return "d" def __eq__(self, other): return isinstance(self, type(other)) def _key(self): return str(self), b = B() Clearly one would expect b.__hash__ to be defined here, since it is defined under Comparable