12 lines
503 B
Markdown
12 lines
503 B
Markdown
# Ledger invariants
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`Ledger.apply(operation_id, account, delta)` applies an operation at most once globally.
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- A successful operation permanently consumes its operation ID.
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- A rejected overdraft must not consume its operation ID.
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- A caller may fund the account and retry the same rejected operation.
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- Balances may never become negative.
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- Duplicate successful operations return the current balance without applying the delta again.
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The current implementation violates the rejected-operation rule.
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