refactor return-by-reference

src/wallet3/keyring.cpp

@@ -114,14 +114,15 @@ namespace wallet
   }
 
   // TODO: replace later when removing wallet2½ layer
-  uint64_t
-  Keyring::output_amount(
+  std::pair<uint64_t, rct::key>
+  Keyring::output_amount_and_mask(
       const rct::rctSig& rv,
       const crypto::key_derivation& derivation,
-      unsigned int i,
-      rct::key& mask)
+      unsigned int i)
   {
-    return wallet25::output_amount(rv, derivation, i, mask, key_device);
+    rct::key mask{};
+    auto amount = wallet25::output_amount(rv, derivation, i, mask, key_device);
+    return {amount, std::move(mask)};
   }
 
   // This gets called for every output in the transaction, there is some complication for how the 

src/wallet3/keyring.hpp

@@ -68,12 +68,11 @@ namespace wallet
         uint64_t output_index,
         const cryptonote::subaddress_index& sub_index);
 
-    virtual uint64_t
-    output_amount(
+    virtual std::pair<uint64_t, rct::key>
+    output_amount_and_mask(
         const rct::rctSig& rv,
         const crypto::key_derivation& derivation,
-        unsigned int i,
-        rct::key& mask);
+        unsigned int i);
 
     virtual crypto::public_key
     generate_output_ephemeral_keys(

src/wallet3/transaction_scanner.cpp

@@ -66,10 +66,9 @@ namespace wallet
         Output o;
 
         // TODO: ringct mask returned by reference.  ugh.
-        auto amount = wallet_keys->output_amount(
-            tx.tx.rct_signatures, derivations[derivation_index], output_index, o.rct_mask);
+        std::tie(o.amount, o.rct_mask) = wallet_keys->output_amount_and_mask(
+            tx.tx.rct_signatures, derivations[derivation_index], output_index);
 
-        o.amount = amount;
         o.key_image = key_image;
         o.subaddress_index = *sub_index;
         o.output_index = output_index;