命令模式是一种行为设计模式。将一系列操作，封装为类（命令），使用队列保存历史命令，实现撤销undo操作。
- Command：抽象命令类。
- ConcreteCommand：具体命令类，依赖Receiver类执行不同命令。
- Invoker：调用者类，持有命令队列，触发命令。
- Receiver：concreteCommand操作的对象，执行具体的命令。
- Client：调用Invoker触发命令。
#include <iostream>
#include <stack>
#include <memory>//底层执行
class Receiver
{
public:Receiver()=default;~Receiver()=default;Receiver(const Receiver& another){this->str_ = another.str_; }Receiver& operator=(Receiver& another){if(&another==this)return *this;this->str_ = another.str_; return *this;}Receiver(Receiver&& another){this->str_ = std::move(another.str_);}Receiver& operator=(Receiver&& another){if(&another==this)return *this;this->str_ = std::move(another.str_);return *this;}std::string Do()const{return str_;}
private:std::string str_{"do something..\n"};
};class Command
{
public:Command()=default;virtual ~Command()=default;virtual void Execute()=0;virtual void Undo()=0;
};//封装底层执行，暴露命令或操作
class PasteCommand:public Command
{
public:PasteCommand(Receiver receiver){receiver_ = std::move(receiver);}virtual void Execute()override{ std::cout<<receiver_.Do()<<"\n";}virtual void Undo()override{std::cout<<"un"<<receiver_.Do()<<"\n";}
private:Receiver receiver_;
};//记录历史操作。触发操作、undo操作。
class Invoker
{
public://通过SetCommand进行依赖注入（或改为构造）void SetCommand(std::unique_ptr<Command> command){this->command_ = std::move(command);}void Click(){command_->Execute();history_.push(std::move(command_));}void Undo(){auto last = std::move(history_.top());last->Undo();history_.pop();}
private:std::unique_ptr<Command> command_{nullptr};std::stack<std::unique_ptr<Command>> history_;
};int main()
{Receiver receiver;std::unique_ptr<Command> upc = std::make_unique<PasteCommand>(receiver);Invoker invoker;invoker.SetCommand(std::move(upc)); invoker.Click();invoker.Undo();return 0;
}