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>

using namespace std;

// 通过闭包实现类似类的结构
auto fun(int x) {
  int* _x = new int(x);
  // toString 函数捕获_x，用以输出当前_x的值
  auto toString = [_x]() -> string { return "x: " + to_string(*_x); };
  // add 函数用于增加_x的值
  auto add = [_x]() { (*_x)++; };
  // remove 函数用于释放_x指向的内存
  auto remove = [_x]() { delete _x; };

  // 结构体内包含三个函数
  struct {
    decltype(toString) toString;
    decltype(add) add;
    decltype(remove) remove;
  } self{toString, add, remove};

  return self;
}

int main() {
  auto obj1 = fun(1);
  auto obj2 = fun(3);
  cout << obj1.toString() << endl;  // 输出 "x: 1"
  obj1.add();                       // 增加obj1的内部_x的值
  cout << obj1.toString() << endl;  // 输出 "x: 2"
  cout << obj2.toString() << endl;  // 输出 "x: 3"
  obj1.remove();                    // 释放obj1的内部_x的内存
  obj2.remove();                    // 释放obj2的内部_x的内存
  return 0;
}

python

def extend(*father_class_list):
  def decorator(sub_class):
    def decorator_class(*args, **kwargs):
      if len(father_class_list) == 0:
          return sub_class(lambda: ...,*args, **kwargs)
      else:
        super_obj = lambda: ...
        for father_class in father_class_list:
          current_super_obj = father_class(super_obj, *args, **kwargs)
          for k,v in current_super_obj.__dict__.items():
            if not k.startswith('__'):
              setattr(super_obj, k, v)
        return sub_class(super_obj, *args, **kwargs)
    return decorator_class
  return decorator
@extend()
def Runner(self, *args, **kwargs):
  self.speed = kwargs.get('speed', 10)
  def run():
    return f'{self.name} is running at {self.speed} km/h'
  self.run = run
  return self
@extend()
def Animal(self, *args,**kwargs):
  self.name = kwargs.get('name', 'Unknown')

  def to_string():
    return f'{self.name} is an animal'

  # bind the method to the object
  self.to_string = to_string
  return self
@extend(Animal,Runner)
def Dog(self, *args, **kwargs):
  self.age = kwargs.get('age', 10)
  self.super_to_string = self.to_string
  def to_string():
    print(self.super_to_string())
    return f'{self.name} is {self.age} years old, running at {self.speed} km/h'

  # bind the method to the object
  self.to_string = to_string
  return self

dog = Dog(name='Rex', age=5)
print(dog.to_string())

"""
运行结果:
Rex is an animal
Rex is 5 years old, running at 10 km/h
"""

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