set
Store the specified continuation in the receiver, which must be a fiber. This is the only circumstance in all of Avail in which a field of a (potentially) shared object may hold a non-shared object.
When we have our own memory manager with thread-specific arenas for the unshared heap, those arenas will be associated with the fiber that was running during their allocation. When the fiber exits, if the fiber was shared, the fiber's result will be copied out to shared space prior to deletion of its arenas. But prior to that time, the shared fiber guards its unshared continuation from prying eyes.
Parameters
field
An enumeration value that defines the field ordering.
a
The object to store at the specified slot.