polymorphism

问题 Here you can see my reduced entity structure which I would like to store in my Sqlite database. I've a Graph which holds a Set of GraphElements . My Graph consists of Edges , Nodes and Loads which are all different Elements. For a deep-first-search for example each node needs to know its neighbor nodes. Therefore I need the NeigborNodes -List. For other functionalities I need also to know the ConnectedElements -List. class Graph { public int Id { get; set; } public string Name { get; set; }

问题 Here you can see my reduced entity structure which I would like to store in my Sqlite database. I've a Graph which holds a Set of GraphElements . My Graph consists of Edges , Nodes and Loads which are all different Elements. For a deep-first-search for example each node needs to know its neighbor nodes. Therefore I need the NeigborNodes -List. For other functionalities I need also to know the ConnectedElements -List. class Graph { public int Id { get; set; } public string Name { get; set; }

问题 I am trying to implement a function that returns a table with the same structure as an input table in the parameter, using PL/pgSQL (PostgreSQL 9.3). Basically, I want to update a table, and return a copy of the updated table with plpgsql. I searched around SO and found several related questions (e.g. Return dynamic table with unknown columns from PL/pgSQL function and Table name as a PostgreSQL function parameter), which lead to the following minimal test example: CREATE OR REPLACE FUNCTION

问题 I am trying to write a generic class to avoid code repetition. I would like to have generic methods for: Get Entity/Model from server by id. Get List of all Entities/Models from server. Send to server and save in db Entity/Model. It should work with Generic classes, e.g.: Services<PizzaProxy> factory = GWT.create(Services.class); factory.initialize(new SimpleEventBus()); GenericContext<PizzaProxy> context = factory.genericContext(); context.get().to(new Receiver<List<GenericProxy<PizzaProxy>>

问题 I am trying to write a generic class to avoid code repetition. I would like to have generic methods for: Get Entity/Model from server by id. Get List of all Entities/Models from server. Send to server and save in db Entity/Model. It should work with Generic classes, e.g.: Services<PizzaProxy> factory = GWT.create(Services.class); factory.initialize(new SimpleEventBus()); GenericContext<PizzaProxy> context = factory.genericContext(); context.get().to(new Receiver<List<GenericProxy<PizzaProxy>>

问题 I would like to write a procedure which takes two passed-object dummy arguments, such as module m type, abstract :: Parent contains procedure(f_Parent), deferred :: f end type abstract interface subroutine f_Parent(foo,bar) import Parent implicit none class(Parent), intent(in) :: foo class(Parent), intent(in) :: bar end subroutine end interface type, extends(Parent) :: Child contains procedure, public :: f => f_Child end type contains subroutine f_Child(foo,bar) implicit none class(Child),

问题 I would like to write a procedure which takes two passed-object dummy arguments, such as module m type, abstract :: Parent contains procedure(f_Parent), deferred :: f end type abstract interface subroutine f_Parent(foo,bar) import Parent implicit none class(Parent), intent(in) :: foo class(Parent), intent(in) :: bar end subroutine end interface type, extends(Parent) :: Child contains procedure, public :: f => f_Child end type contains subroutine f_Child(foo,bar) implicit none class(Child),

问题 How can I create an array which can hold objects of different classes in C++? 回答1: If you want to create your own, wrap access to a pointer/array using templates and operator overloading. Below is a small example: #include <iostream> using namespace std; template <class T> class Array { private: T* things; public: Array(T* a, int n) { things = new T[n]; for (int i=0; i<n; i++) { things[i] = a[i]; } } ~Array() { delete[] things; } T& operator [](const int idx) const { return things[idx]; } };

问题 I'm trying to implement a "polymorphic" Input enum which hides whether we're reading from a file or from a stdin. More concretely, I'm trying build an enum that will have a lines method that will in turn "delegate" that call to either a File wrapped into a BufReader or to a StdInLock (both of which have the lines() method). Here's the enum: enum Input<'a> { Console(std::io::StdinLock<'a>), File(std::io::BufReader<std::fs::File>) } I have three methods: from_arg for deciding whether we're

问题 I'm trying to implement a "polymorphic" Input enum which hides whether we're reading from a file or from a stdin. More concretely, I'm trying build an enum that will have a lines method that will in turn "delegate" that call to either a File wrapped into a BufReader or to a StdInLock (both of which have the lines() method). Here's the enum: enum Input<'a> { Console(std::io::StdinLock<'a>), File(std::io::BufReader<std::fs::File>) } I have three methods: from_arg for deciding whether we're