Other

In Game Maker and in ENIGMA, other is a keyword
representing another instance involved in a block of code. This varies
by context:

• In a collision event, other
  represents the instance with which the current instance is colliding
  (literally the other object involved).
• In a with() statement, the scope is
  changed, and other represents the instance owning the calling
  scope. For example, if object0 says with (object1) {newscope}, other will be an instance of object0 inside
  newscope.
• In an "applied" Action tile, other behaves
  the same way as in with(), referring to the calling instance.

Implementation

ENIGMA stores the current scope's calling instance in
enigma::instance_event_iterator. Alongside that, it keeps a stack of
struct iterator_level, which always contains a pointer to
instance_event_iterator at its bottom. Finally, it stores
enigma::instance_other to directly represent the most recently lost
scope.

This stack is most easily manipulated by instantiating struct enigma::with_iter. In fact, that structure operates with()
entirely:

  #define with(x) for (enigma::with_iter ENIGMA_WITHITER(enigma::fetch_inst_iter_by_int(x),enigma::instance_event_iterator->inst); \
    enigma::instance_event_iterator; enigma::instance_event_iterator = enigma::instance_event_iterator->next)

Upon instantiation, with_iter pushes the iterator_level stack with
the variables mentioned above. Upon deconstruction, it pops the stack,
restoring both variables to their original state.