command pattern in C++

```
#include <iostream>
using namespace std;

class Command {
public:
    virtual ~Command() { }
    virtual void Execute() const = 0;
};

class SimpleCommand : public Command {
private:
    string pay_load_;

public:
    explicit SimpleCommand(std::string pay_load) : pay_load_(pay_load) { }
    void Execute() const override {
        cout << "SimpleCommand: printing (" << this->pay_load_ << ")\n";
    }
};

class Receiver {
 public:
  void DoSomething(const std::string &a) {
    cout << "Receiver: Working on (" << a << ".)\n";
  }
  void DoSomethingElse(const std::string &b) {
    cout << "Receiver: Also working on (" << b << ".)\n";
  }
};

class ComplexCommand : public Command {
private:
  Receiver *receiver_;
  std::string a_;
  std::string b_;
public:
  ComplexCommand(Receiver *receiver, std::string a, std::string b) : receiver_(receiver), a_(a), b_(b) {}
  void Execute() const override {
    cout << "ComplexCommand: Complex stuff should be done by a receiver object.\n";
    this->receiver_->DoSomething(this->a_);
    this->receiver_->DoSomethingElse(this->b_);
  }
};

class Invoker {
private:
  Command *on_start_;
  Command *on_finish_;

public:
  ~Invoker() {
    delete on_start_;
    delete on_finish_;
  }

  void SetOnStart(Command *command) {
    this->on_start_ = command;
  }
  void SetOnFinish(Command *command) {
    this->on_finish_ = command;
  }
  void DoSomethingImportant() {
    std::cout << "Invoker: Does anybody want something done before I begin?\n";
    if (this->on_start_) {
      this->on_start_->Execute();
    }
    cout << "Invoker: ...doing something really important...\n";
    cout << "Invoker: Does anybody want something done after I finish?\n";
    if (this->on_finish_) {
      this->on_finish_->Execute();
    }
  }
};

int main() {
  Invoker *invoker = new Invoker;
  invoker->SetOnStart(new SimpleCommand("Say Hi!"));

  Receiver *receiver = new Receiver;
  invoker->SetOnFinish(new ComplexCommand(receiver, "Send email", "Save report"));
  invoker->DoSomethingImportant();

  delete invoker;
  delete receiver;

  return 0;
}

/*
Invoker: Does anybody want something done before I begin?
SimpleCommand: printing (Say Hi!)
Invoker: ...doing something really important...
Invoker: Does anybody want something done after I finish?
ComplexCommand: Complex stuff should be done by a receiver object.
Receiver: Working on (Send email.)
Receiver: Also working on (Save report.)
*/
```
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