Make GetEntriesForConflicts return std::optional

Avoids reusing err_string.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/policy/rbf.h b/src/policy/rbf.h
index a67e9058df..2a41ca8892 100644
--- a/src/policy/rbf.h
+++ b/src/policy/rbf.h
@@ -40,14 +40,13 @@ RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx);
  * mempool must not exceed a total of 100 transactions." Quit as early as possible. There cannot be
  * more than MAX_BIP125_REPLACEMENT_CANDIDATES potential entries.
  * @param[in]   setIterConflicting  The set of iterators to mempool entries.
- * @param[out]  err_string          Used to return errors, if any.
  * @param[out]  allConflicting      Populated with all the mempool entries that would be replaced,
  *                                  which includes descendants of setIterConflicting. Not cleared at
  *                                  the start; any existing mempool entries will remain in the set.
- * @returns false if Rule 5 is broken.
+ * @returns an error message if Rule #5 is broken, otherwise a std::nullopt.
  */
-bool GetEntriesForConflicts(const CTransaction& tx, CTxMemPool& m_pool,
-                            const CTxMemPool::setEntries& setIterConflicting,
-                            CTxMemPool::setEntries& allConflicting,
-                            std::string& err_string) EXCLUSIVE_LOCKS_REQUIRED(m_pool.cs);
+std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx, CTxMemPool& m_pool,
+                                                  const CTxMemPool::setEntries& setIterConflicting,
+                                                  CTxMemPool::setEntries& allConflicting)
+                                                  EXCLUSIVE_LOCKS_REQUIRED(m_pool.cs);
 #endif // BITCOIN_POLICY_RBF_H