Double square brackets in fauxmo.onSetState([]( . . .

What are the square brackets for in this line below ?

fauxmo.onSetState([](unsigned char device_id, const char * device_name, bool state, unsigned char value) {

Thank you.

That indicates the argument is a lambda function. Google "c++ lambda function" and find a good tutorial. It's a fairly advanced concept.

Regards,
Ray L.