refactor: introduce a python-like enumerate() method, and use it in block_reward_reallocation_tests.cpp

src/Makefile.am

@@ -293,6 +293,7 @@ BITCOIN_CORE_H = \
   util/bip32.h \
   util/bytevectorhash.h \
   util/check.h \
+  util/enumerate.h \
   util/error.h \
   util/fees.h \
   util/golombrice.h \

src/test/block_reward_reallocation_tests.cpp

@@ -23,6 +23,7 @@
 #include <llmq/blockprocessor.h>
 #include <llmq/chainlocks.h>
 #include <llmq/instantsend.h>
+#include <util/enumerate.h>
 
 #include <boost/test/unit_test.hpp>
 
@@ -48,10 +49,9 @@ struct TestChainBRRBeforeActivationSetup : public TestChainSetup
 static SimpleUTXOMap BuildSimpleUtxoMap(const std::vector<CTransactionRef>& txs)
 {
     SimpleUTXOMap utxos;
-    for (size_t i = 0; i < txs.size(); i++) {
-        auto& tx = txs[i];
-        for (size_t j = 0; j < tx->vout.size(); j++) {
-            utxos.try_emplace(COutPoint(tx->GetHash(), j), std::make_pair((int)i + 1, tx->vout[j].nValue));
+    for (auto [i, tx] : enumerate(txs)) {
+        for (auto [j, output] : enumerate(tx->vout)) {
+            utxos.try_emplace(COutPoint(tx->GetHash(), j), std::make_pair((int)i + 1, output.nValue));
         }
     }
     return utxos;
@@ -104,9 +104,9 @@ static void SignTransaction(const CTxMemPool& mempool, CMutableTransaction& tx,
     FillableSigningProvider tempKeystore;
     tempKeystore.AddKeyPubKey(coinbaseKey, coinbaseKey.GetPubKey());
 
-    for (size_t i = 0; i < tx.vin.size(); i++) {
+    for (auto [i, input] : enumerate(tx.vin)) {
         uint256 hashBlock;
-        CTransactionRef txFrom = GetTransaction(/* block_index */ nullptr, &mempool, tx.vin[i].prevout.hash, Params().GetConsensus(), hashBlock);
+        CTransactionRef txFrom = GetTransaction(/* block_index */ nullptr, &mempool, input.prevout.hash, Params().GetConsensus(), hashBlock);
         BOOST_ASSERT(txFrom);
         BOOST_ASSERT(SignSignature(tempKeystore, *txFrom, tx, i, SIGHASH_ALL));
     }

src/util/enumerate.h

@@ -0,0 +1,40 @@
+// Copyright (c) 2022 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_ENUMERATE_H
+#define BITCOIN_UTIL_ENUMERATE_H
+
+#include <tuple>
+#include <iterator>
+
+/**
+ * similar to python's enumerate(iterable).
+ * @tparam T type of iterable, automatically deduced
+ * @tparam TIter
+ * @param iterable an iterable object, can be a temporary
+ * @return struct containing a size_t index, and it's element in iterable
+ */
+template <typename T,
+          typename TIter = decltype(std::begin(std::declval<T>())),
+          typename = decltype(std::end(std::declval<T>()))>
+constexpr auto enumerate(T && iterable)
+{
+    struct iterator
+    {
+        size_t i;
+        TIter iter;
+        bool operator != (const iterator & other) const { return iter != other.iter; }
+        void operator ++ () { ++i; ++iter; }
+        auto operator * () const { return std::tie(i, *iter); }
+    };
+    struct iterable_wrapper
+    {
+        T iterable;
+        auto begin() { return iterator{ 0, std::begin(iterable) }; }
+        auto end() { return iterator{ 0, std::end(iterable) }; }
+    };
+    return iterable_wrapper{ std::forward<T>(iterable) };
+}
+
+#endif // BITCOIN_UTIL_ENUMERATE_H