op.cpp

class Memory {
public:
  Memory(std::array<uint8_t, 1024> b) { buff_ = std::move(b); }
  
  uint16_t& operator[](uint16_t addr) {
    return (buff_[addr] << 8) + buff_[addr + 1]; // This doesn't work
    // cannot bind non-const lvalue reference of type ‘uint16_t& {aka short unsigned int&}’ to an rvalue of type ‘uint16_t {aka short unsigned int}’
  }
  
private:
  std::array<uint8_t, 1024> buff_;
};