A simple system for making an ordered list of instances.

§1. Here's how to place the instance objects in order. The ordering is used not only for compilation, but also for instance counting (e.g., marking the black gate as the 8th instance of "door"), so it's needed earlier than the compilation phase, too.

They are stored as a linked list with the links in an array indexed by the allocation IDs of the objects. This could all now alternatively be done with the linked_list type provided by foundation, but never mind: it works.

instance *first_instance_in_list = NULL;
instance **next_instance_in_current_list = NULL;
instance *last_instance_in_list = NULL;

§2. To build the list, first call OrderingInstances::begin then repeatedly OrderingInstances::place_next.

void OrderingInstances::begin?Usage of OrderingInstances::begin:
§3(void) {
    int i, nc = NUMBER_CREATED(instance);
    if (next_instance_in_current_list == NULL) {
        next_instance_in_current_list = (instance **)
            (Memory::calloc(nc, sizeof(instance *), OBJECT_COMPILATION_MREASON));
    }
    for (i=0; i<nc; i++) next_instance_in_current_list[i] = NULL;
    first_instance_in_list = NULL;
    last_instance_in_list = NULL;
}

void OrderingInstances::place_next?Usage of OrderingInstances::place_next:
§3(instance *I) {
    if (last_instance_in_list == NULL)
        first_instance_in_list = I;
    else
        next_instance_in_current_list[last_instance_in_list->allocation_id] = I;
    last_instance_in_list = I;
}

§3. For instance, here we put them in order of definition, which is the default:

void OrderingInstances::objects_in_definition_sequence(void) {
    OrderingInstances::begin();
    instance *I;
    LOOP_OVER_INSTANCES(I, K_object)
        OrderingInstances::place_next(I);
}

§4. And we read the order back using these macros:

define FIRST_IN_INSTANCE_ORDERING first_instance_in_list
define NEXT_IN_INSTANCE_ORDERING(I) next_instance_in_current_list[I->allocation_id]
define LOOP_THROUGH_INSTANCE_ORDERING(I)
    for (I=FIRST_IN_INSTANCE_ORDERING; I; I=NEXT_IN_INSTANCE_ORDERING(I))