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闭包实现类

KSJ2023/8/2About 7 minOIMODInt

闭包实现类

你是否曾经想过，不用类也能封装数据和方法？这篇文章将带你走进闭包的奇妙世界，展示如何用闭包来实现这一点。通过一个有趣的代码示例，你将看到闭包是如何捕获变量并提供类似类的功能的。准备好了吗？让我们开始这段有趣的旅程吧！

cpp
#include <iostream>
#include <string>
#include <functional>
#include <vector>
#include <memory>

using namespace std;

// 1. 封装 (Encapsulation) - 状态_x被封装在闭包中
auto createCounter(int x) {
    int* _x = new int(x);
    auto toString = [_x]() -> string { return "Counter x: " + to_string(*_x); };
    auto add = [_x]() { (*_x)++; };
    auto remove = [_x]() { delete _x; };

    struct Counter {
        function<string()> toString;
        function<void()> add;
        function<void()> remove;
    };
    return Counter{toString, add, remove};
}

// 2. 抽象 (Abstraction) - 定义一个“形状”的抽象接口
struct Shape {
    function<string()> toString;
    function<double()> area;
    function<void()> draw;
};

// 3. 继承 (Inheritance) 和 多态 (Polymorphism)
// 基“类”工厂函数：ShapeBase
auto ShapeBase(const string& name, double value) {
    string* _name = new string(name);
    double* _value = new double(value);

    // 基类的公共方法
    auto baseToString = [_name]() -> string { return "Shape: " + * _name; };
    auto baseGetValue = [_value]() -> double { return * _value; };
    auto baseRemove = [_name, _value]() {
        delete _name;
        delete _value;
    };

    struct Base {
        function<string()> toString;
        function<double()> getValue;
        function<void()> remove;
    };
    return Base{baseToString, baseGetValue, baseRemove};
}

// 派生“类”1: Circle，继承自ShapeBase，并实现area和draw
auto createCircle(const string& name, double radius) {
    // 组合：捕获基类实例，模拟继承
    auto base = ShapeBase(name, radius);
    auto area = [base]() -> double {
        double r = base.getValue();
        return 3.14159 * r * r;
    };
    auto draw = [base, area]() {
        cout << "Drawing Circle: " << base.toString() << ", area: " << area() << endl;
    };
    // 重写toString，添加派生类信息
    auto toString = [base]() -> string {
        return base.toString() + " (Circle)";
    };
    auto remove = [base]() { base.remove(); };

    return Shape{toString, area, draw};
}

// 派生“类”2: Square，继承自相同的抽象接口，但不同实现
auto createSquare(const string& name, double side) {
    auto base = ShapeBase(name, side);
    auto area = [base]() -> double {
        double s = base.getValue();
        return s * s;
    };
    auto draw = [base, area]() {
        cout << "Drawing Square: " << base.toString() << ", area: " << area() << endl;
    };
    auto toString = [base]() -> string {
        return base.toString() + " (Square)";
    };
    auto remove = [base]() { base.remove(); };

    return Shape{toString, area, draw};
}

int main() {
    cout << "=== 1. 封装示例 ===" << endl;
    auto counter = createCounter(5);
    cout << counter.toString() << endl; // x: 5
    counter.add();
    cout << counter.toString() << endl; // x: 6
    counter.remove();

    cout << "\n=== 2. 抽象、继承与多态示例 ===" << endl;
    // 多态：将不同的派生类对象统一存放在基类抽象接口的容器中
    vector<Shape> shapes;
    shapes.push_back(createCircle("MyCircle", 3.0));
    shapes.push_back(createSquare("MySquare", 2.5));

    for (auto& shape : shapes) {
        // 同一接口，不同行为
        cout << shape.toString() << ", Area: " << shape.area() << endl;
        shape.draw(); // 多态调用
        cout << "---" << endl;
    }

    // 释放资源
    for (auto& shape : shapes) {
        // 通常remove需要被调用，这里演示，实际需注意生命周期管理
        // shape.remove(); // 此例中shape持有base的副本，base.remove会释放资源
        // 更安全的做法是使用智能指针，但示例为展示闭包机制，暂不引入
    }

    return 0;
}
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