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Using Regular DGD Objects and LWOs — Swapping Behavior

Before dealing specifically with LWOs, make sure you understand DGD's normal swapping behavior.

An LWO is an object which is 'embedded' in another DGD object. Regular DGD objects swap as usual, but an LWO swaps as part of another object's data. When the LWO's 'parent' object (not in an inheritance sense, but in the sense of whose data space contains references to it) is swapped out, so is the LWO. The LWO doesn't get its own sectors in the swapfile. Instead, the LWO is part of the space taken up by its host object.

Like an array or mapping, an LWO is copied if an object (other than its host object) has a reference to it at the end of a thread of execution. That is, the LWO is referenced by more than one regular DGD object for no longer than one thread of execution. After that, it is copied. Be careful passing references to LWOs around for this reason — you don't want duplicate copies, which are large, wasteful and may cause data inconsistencies.

Like arrays or mappings, LWOs are garbage collected, so when the last reference to them disappears, so do they. This is true even in circular structures. LWOs may not be explicitly destructed.

LWOs cannot be used as an editor, user or parser object, nor can they have callouts. It is not clear (to me, right this second) whether a parse_string() call in an LWO will store its generated automaton cache in the LWO or the host heavyweight DGD object. If the master object of an LWO is destructed, the LWO is destroyed as well, along with all others created from that master object.

If you've been looking for structures in DGD, LWOs fill roughly that need.