如何单独和同时与 C++ class 成员一起工作？

Question

我有以下 C++ 代码

矩形.h

class Rectangle {
public:
    Rectangle(int _id);
    void draw();
    int getId();
private:
    int id;
};

矩形.cpp

#include "Rectangle.h"
#include <iostream>

Rectangle::Rectangle(int _id) {
    id = _id;
}
void Rectangle::draw() {
    std::cout << "Drawing rectangle with id: " << id << std::endl;
}

int Rectangle::getId() {
    return id;
}

矩形集合.h

#include "Rectangle.h"

class RectanglesCollection {
public:
    Rectangle rectangle_00;
    Rectangle rectangle_01;
    Rectangle rectangle_02;
    Rectangle rectangle_03;
        
    RectanglesCollection();
        
    void update();
};

矩形集合.cpp

#include "RectanglesCollection.h"

RectanglesCollection::RectanglesCollection() : 
rectangle_00(10),
rectangle_01(20),
rectangle_02(30),
rectangle_03(40)
{}
    
void RectanglesCollection::update() 
{
    rectangle_00.draw();
    rectangle_01.draw();
    rectangle_02.draw();
    rectangle_03.draw();
}

主文件

#include "Rectangle.h"
#include "RectanglesCollection.h"
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char** argv) {

    RectanglesCollection rectangles;
    rectangles.update();
    
    std::cout << "Id of the first rectangle in collection of rectangles: " << rectangles.rectangle_00.getId() << std::endl;
    
    return 0;
}

我的问题是我是否有可能避免在RectanglesCollection::update方法中重复代码，而不是使用一些循环直接在各个Rectangle成员之上进行迭代？ 如果集合的用户除了定义Rectangle class 的实例之外不需要做任何其他事情，那将是理想的。 同时，我想保留与 Rectangle 成员单独合作的可能性，例如rectangles.rectangle_00.getId() 。

Answer 1

如果您将 Rectangle 成员变量表示为 RectanglesCollection 中的std::array<Rectangle, 4> ，则可以通过索引和operator[](size_t)访问器成员 function 轻松访问它们。

#include <array>
#include <cstddef>
#include <iostream>
#include <stdexcept>

using std::array;
using std::cout;
using std::ostream;
using std::out_of_range;
using std::size_t;

// NAME_OF for String-ify.
#define NAME_OF(x) #x

class Rectangle {
    int _id;
public:
    Rectangle(int id);
    void draw(ostream&) const;
    auto id() const -> int;
};

Rectangle::Rectangle(int id_) : _id{id_} { }

void Rectangle::draw(ostream& out) const {
    out << "Drawing rectangle with id: " << id() << "\n";
}

auto Rectangle::id() const -> int {
    return _id;
}

class RectanglesCollection {
    array<Rectangle, 4> rectangles = {10, 20, 30, 40};
public:
    auto operator[](size_t i) const -> Rectangle;
    void display() const;
};

auto RectanglesCollection::operator[](size_t i) const -> Rectangle {
    if (i >= rectangles.size())
        throw out_of_range(NAME_OF(i));

    return rectangles[i];
}

void RectanglesCollection::display() const {
    for (auto&& r : rectangles) {
        r.draw(cout);
    }
}

int main() {
    auto rectangles = RectanglesCollection();
    rectangles.display();
    cout << "Id of the first rectangle in collection of rectangles: " << rectangles[0].id() << "\n";
}