Custom Kaleidoscope Plugin for `alt`+`A` to switch apps (on macOS)

AppSwitcher.ino

namespace kaleidoscope {
namespace plugin {
class AppSwitcher : public kaleidoscope::Plugin {
 public:
  static constexpr KeyAddr invalid_addr{KeyAddr::invalid_state};

  AppSwitcher() {}

  EventHandlerResult onKeyswitchEvent(Key &key,
                                      KeyAddr key_addr,
                                      uint8_t key_state) {
    if (keyToggledOn(key_state)) {
      if (key == Key_LeftAlt) {
        alt_key_addr_ = key_addr;
      } else if (key == Key_A && alt_key_addr_ != invalid_addr) {
        // release `alt`
        handleKeyswitchEvent(Key_NoKey, alt_key_addr_, WAS_PRESSED);
        // press `gui`
        handleKeyswitchEvent(Key_LeftGui, alt_key_addr_, IS_PRESSED);
        key = Key_Tab;
        alt_key_addr_ = invalid_addr;
      }
    }
    return EventHandlerResult::OK;
  }
 private:
  KeyAddr alt_key_addr_;
};
} // namespace plugin
} // namespace kaleidoscope

kaleidoscope::plugin::AppSwitcher AppSwitcher;

KALEIDOSCOPE_INIT_PLUGINS(
  Appswitcher, …
)