Writing a store

An application that keeps its exchanges elsewhere than in memory or in the bundle's tables implements the stores. Each contract is also a test case in the library's tests — ReservationStoreTestCase, TransferLogTestCase, OfferStoreTestCase — that a store's test extends.

ReservationStore

• add() writes a reservation once per key — false when the key is there — and checks the units of the reward's reserved and confirmed reservations against the stock and the member's limit in the same step, so that two members never get the last unit: under a lock, or in one statement.
• settle() moves a reservation out of reserved only while it is reserved, and says whether this call did.
• discard() deletes a reservation still reserved; held(), due(), ofMember() and eraseMember() read and erase.

TransferLog

record() writes a transfer once per key; given() sums what a member gave in a currency over a period; ofMember(), latest() and eraseMember() read and erase.

OfferStore

• open() writes an offer once per key — false when the key is there — and holds its offered items in the same step, refusing with Refusal::AlreadyHeld an item another open offer holds.
• close() moves an offer out of open only while it is open, releases its items, and says whether this call did.
• holder(), made(), due(), ofMember() and eraseMember() read and erase.

Transaction and Inventory

A Transaction runs the steps of an acceptance or a counter-offer as one unit; with a database, one of its transactions. An Inventory tells an item's owner and whether it may change hands, and moves the items of an accepted trade all together, refusing with Refusal::NotOwned an item that no longer belongs to its giver.