harakiri.h

#include <utility>
#include <memory>
#include <string>
#include <type_traits>

class OneTimeCallback {
protected:
    std::unique_ptr<std::string> s_;

public:
    OneTimeCallback(const char *);

    OneTimeCallback(std::string);

    virtual ~OneTimeCallback();

    virtual const std::string operator()() const &&;
};

class AwesomeCallback : public OneTimeCallback {
public:
    AwesomeCallback(std::string s);
    AwesomeCallback(const char *s);
    ~AwesomeCallback();

    const std::string operator()() const &&;
};