成员变量是类的对象，通过初始化列表来初始化

class Hc595 {
      using FuncVoidVoid = void (*)(void);
      using FuncVoidBool = void (*)(bool);

public:
      Hc595(FuncVoidVoid sck, FuncVoidVoid rck, FuncVoidBool bit, FuncVoidBool oe, FuncVoidVoid bit_delay) :
	      sck_(sck), rck_(rck), bit_(bit), oe_(oe), bit_delay_(bit_delay) {};

      void ShiftByte(uint8_t b);

      void Store();

      void Display(bool en);

private:
      FuncVoidVoid sck_;
      FuncVoidVoid rck_;
      FuncVoidBool bit_;
      FuncVoidBool oe_;
      FuncVoidVoid bit_delay_;
};

class Led {
public:
      enum LedIndex {
	      kLed1 = 0, kLed2, kLed3, kLed4, kLed5, kLed6,
	      kLed7, kLed8, kLed9, kLed10, kLed11, kLed12,
      };
public:
      Led();
      void Set(LedIndex index, bool g, bool r, bool b);
      void Refresh();
      void ClearData();

private:
      static const uint8_t kDataLength = 12;
      static const uint8_t kBufLength = 5;
      std::array<uint8_t, kDataLength> data_ {};
      std::array<uint8_t, kBufLength> buf_ {};
      Hc595 hc_;
};

Led::Led() : hc_({SckRiseEdge, RckRiseEdge, DataBitPinControl, nullptr, nullptr})
{
      //hc_ = {SckRiseEdge, RckRiseEdge, DataBitPinControl, nullptr, nullptr};

      hc_.Display(true);
}