In the settings, we have the handler that allows to call a function to set the value.
We need the same mecanism to get the value: a getter.

This getter should return a float, to be consistent with the current system.

Current situation

Let's take an example with this setting:

<dl_setting var="autopilot.kill_throttle" min="0" step="1" max="1" module="autopilot" values="Resurrect|Kill" handler="KillThrottle"/>

#define DlSetting(_idx, _value) { \
  switch (_idx) { \
     ...
    case 13: autopilot_KillThrottle( _value ); _value = autopilot.kill_throttle; break;\
    }\
}

#define PeriodicSendDlValue(_trans, _dev) { \
     ...
    case 13: var = autopilot.kill_throttle; break;\
    ...
}

static inline float settings_get_value(uint8_t i) {
  ...
  case 13: return autopilot.kill_throttle;
  ...
}

⚠️ First of all even in the current system, I think _value = autopilot.kill_throttle; (line 4) should be removed: If there is a handler, the value should not be forcefully changed after calling the handler.

Proposed new behavior

The setting could be changed like this:

<dl_setting name="KillThrottle" getter="getKillThrottle()" min="0" step="1" max="1" values="Resurrect|Kill" handler="KillThrottle"/>

It would result in this generated code:

#define DlSetting(_idx, _value) { \
  switch (_idx) { \
     ...
    case 13: KillThrottle( _value ); break;\
    }\
}

#define PeriodicSendDlValue(_trans, _dev) { \
     ...
    case 13: var = getKillThrottle(); break;\
    ...
}

static inline float settings_get_value(uint8_t i) {
  ...
  case 13: return getKillThrottle();
  ...
}

Defining the getter like this getter="getKillThrottle()" allows to specify either a function call, or a global variable like in the current situation.

The name attribute would be added to define the name of the setting. shortname would be deprecated in favor of name.
The name resolution order would be: name, shortname (with deprecated warning), var.

XML valid cases

<dl_setting var="autopilot.kill_throttle" min="0" step="1" max="1" values="Resurrect|Kill"/>

<dl_setting name="KillThrottle" var="autopilot.kill_throttle" min="0" step="1" max="1" values="Resurrect|Kill" handler="KillThrottle"/>

<dl_setting name="KillThrottle" getter="getKillThrottle()" min="0" step="1" max="1" values="Resurrect|Kill" handler="KillThrottle"/>

<dl_setting name="KillThrottle" var="autopilot.kill_throttle" getter="getKillThrottle()" min="0" step="1" max="1" values="Resurrect|Kill"/>

The following should Fail at compilation, because var would be unused:

<dl_setting var="autopilot.kill_throttle" getter="getKillThrottle()" min="0" step="1" max="1" values="Resurrect|Kill" handler="KillThrottle"/>