c++ - 如何将 std::function 的零个或多个参数用作 std::map 中的值？

Question

我有一个 Engine 类，它有一个 std::map 类型的成员，它将枚举映射到成员函数。 如果函数的参数数量相同，我可以将枚举映射到所有函数。

enum STATE { OFF, ON, HIBERNATE, RESTART };
enum RETCODE { SUCCESS, FAIL, UNKNOWN, OUTOFBOUND };

class Engine
{
    Engine();
    RETCODE StateOn(double val);
    RETCODE StateOff(double val);
    RETCODE StateHibernate(double val);
    RETCODE StateRestart(double val);
private:
    const std::map<STATE, std::function<RETCODE(double)>> Map_State_FnPtr;
};

Engine::Engine() : Map_State_FnPtr {
        { STATE::ON, [=](double val) {return StateOn(val); } },
        { STATE::OFF, [=](double val) {return StateOff(val); } },
        { STATE::HIBERNATE, [=](double val) {return StateHibernate(val); } },
        { STATE::RESTART, [=](double val) {return StateRestart(val); } }
    }
{
    // c'tor body
}

但我有一个场景，其中某些函数可以有零个或多个参数。 在这种情况下如何声明和构造映射变量？

class Engine
{
    Engine();
    RETCODE StateOn();                                              // No arguments
    RETCODE StateOff(double val);                                   // 1 argument
    RETCODE StateHibernate(double val, const std::string & data);   // Multiple arguments
    RETCODE StateRestart(double val);
private:
    const std::unordered_map<STATE, std::function<RETCODE()>> Map_State_FnPtr; // What should be the declaration?
};

对于这种情况还有其他建议吗？ 请帮忙。

Answer 1

您始终可以忽略参数

{
    { STATE::ON, [=](double, const std::string &) {return StateOn(); } },
    { STATE::OFF, [=](double val, const std::string &) {return StateOff(val); } },
    { STATE::HIBERNATE, [=](double val, const std::string & data) {return StateHibernate(val, data); } },
    { STATE::RESTART, [=](double val, const std::string &) {return StateRestart(val); } }
}