Why not use: x = !x;?

[bperrybap]

@in0

The first production release with CHANGE was ArduinoCore-API 1.1.0:
Fix some cross-stuff · arduino/ArduinoCore-API@445594a · GitHub

So you can use the ARDUINO_API_VERSION macro for this purpose:
ArduinoCore-API/api/ArduinoAPI.h at 1.1.0 · arduino/ArduinoCore-API · GitHub

#if !defined(ARDUINO_API_VERSION) || ARDUINO_API_VERSION < 10100
// handle absence of CHANGE
#endif

That looks like it would work for now for the arduino.cc platforms, but I'm not sure if that will always work across other platforms from 3rd party core developers.

i.e. it is possible that a platform may add CHANGE pin support without fully implementing the ArduinoAPI stuff.

So over time, it may start to get trick/ugly to detect it across platforms.

--- bill