partial bitcoin#16889: Add some general std::vector utility functions

src/Makefile.am

@@ -267,6 +267,7 @@ BITCOIN_CORE_H = \
   util/string.h \
   util/time.h \
   util/threadnames.h \
+  util/vector.h \
   validation.h \
   validationinterface.h \
   versionbits.h \

src/bech32.cpp

@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <bech32.h>
+#include <util/vector.h>
 
 namespace
 {
@@ -24,13 +25,6 @@ const int8_t CHARSET_REV[128] = {
      1,  0,  3, 16, 11, 28, 12, 14,  6,  4,  2, -1, -1, -1, -1, -1
 };
 
-/** Concatenate two byte arrays. */
-data Cat(data x, const data& y)
-{
-    x.insert(x.end(), y.begin(), y.end());
-    return x;
-}
-
 /** This function will compute what 6 5-bit values to XOR into the last 6 input values, in order to
  *  make the checksum 0. These 6 values are packed together in a single 30-bit integer. The higher
  *  bits correspond to earlier values. */

src/test/util_tests.cpp

@@ -11,6 +11,7 @@
 #include <util/string.h>
 #include <util/moneystr.h>
 #include <test/test_dash.h>
+#include <util/vector.h>
 
 #include <stdint.h>
 #include <vector>
@@ -1162,4 +1163,109 @@ BOOST_AUTO_TEST_CASE(test_DirIsWritable)
     fs::remove(tmpdirname);
 }
 
+namespace {
+
+struct Tracker
+{
+    //! Points to the original object (possibly itself) we moved/copied from
+    const Tracker* origin;
+    //! How many copies where involved between the original object and this one (moves are not counted)
+    int copies;
+
+    Tracker() noexcept : origin(this), copies(0) {}
+    Tracker(const Tracker& t) noexcept : origin(t.origin), copies(t.copies + 1) {}
+    Tracker(Tracker&& t) noexcept : origin(t.origin), copies(t.copies) {}
+    Tracker& operator=(const Tracker& t) noexcept
+    {
+        origin = t.origin;
+        copies = t.copies + 1;
+        return *this;
+    }
+    Tracker& operator=(Tracker&& t) noexcept
+    {
+        origin = t.origin;
+        copies = t.copies;
+        return *this;
+    }
+};
+
+}
+
+BOOST_AUTO_TEST_CASE(test_tracked_vector)
+{
+    Tracker t1;
+    Tracker t2;
+    Tracker t3;
+
+    BOOST_CHECK(t1.origin == &t1);
+    BOOST_CHECK(t2.origin == &t2);
+    BOOST_CHECK(t3.origin == &t3);
+
+    auto v1 = Vector(t1);
+    BOOST_CHECK_EQUAL(v1.size(), 1);
+    BOOST_CHECK(v1[0].origin == &t1);
+    BOOST_CHECK_EQUAL(v1[0].copies, 1);
+
+    auto v2 = Vector(std::move(t2));
+    BOOST_CHECK_EQUAL(v2.size(), 1);
+    BOOST_CHECK(v2[0].origin == &t2);
+    BOOST_CHECK_EQUAL(v2[0].copies, 0);
+
+    auto v3 = Vector(t1, std::move(t2));
+    BOOST_CHECK_EQUAL(v3.size(), 2);
+    BOOST_CHECK(v3[0].origin == &t1);
+    BOOST_CHECK(v3[1].origin == &t2);
+    BOOST_CHECK_EQUAL(v3[0].copies, 1);
+    BOOST_CHECK_EQUAL(v3[1].copies, 0);
+
+    auto v4 = Vector(std::move(v3[0]), v3[1], std::move(t3));
+    BOOST_CHECK_EQUAL(v4.size(), 3);
+    BOOST_CHECK(v4[0].origin == &t1);
+    BOOST_CHECK(v4[1].origin == &t2);
+    BOOST_CHECK(v4[2].origin == &t3);
+    BOOST_CHECK_EQUAL(v4[0].copies, 1);
+    BOOST_CHECK_EQUAL(v4[1].copies, 1);
+    BOOST_CHECK_EQUAL(v4[2].copies, 0);
+
+    auto v5 = Cat(v1, v4);
+    BOOST_CHECK_EQUAL(v5.size(), 4);
+    BOOST_CHECK(v5[0].origin == &t1);
+    BOOST_CHECK(v5[1].origin == &t1);
+    BOOST_CHECK(v5[2].origin == &t2);
+    BOOST_CHECK(v5[3].origin == &t3);
+    BOOST_CHECK_EQUAL(v5[0].copies, 2);
+    BOOST_CHECK_EQUAL(v5[1].copies, 2);
+    BOOST_CHECK_EQUAL(v5[2].copies, 2);
+    BOOST_CHECK_EQUAL(v5[3].copies, 1);
+
+    auto v6 = Cat(std::move(v1), v3);
+    BOOST_CHECK_EQUAL(v6.size(), 3);
+    BOOST_CHECK(v6[0].origin == &t1);
+    BOOST_CHECK(v6[1].origin == &t1);
+    BOOST_CHECK(v6[2].origin == &t2);
+    BOOST_CHECK_EQUAL(v6[0].copies, 1);
+    BOOST_CHECK_EQUAL(v6[1].copies, 2);
+    BOOST_CHECK_EQUAL(v6[2].copies, 1);
+
+    auto v7 = Cat(v2, std::move(v4));
+    BOOST_CHECK_EQUAL(v7.size(), 4);
+    BOOST_CHECK(v7[0].origin == &t2);
+    BOOST_CHECK(v7[1].origin == &t1);
+    BOOST_CHECK(v7[2].origin == &t2);
+    BOOST_CHECK(v7[3].origin == &t3);
+    BOOST_CHECK_EQUAL(v7[0].copies, 1);
+    BOOST_CHECK_EQUAL(v7[1].copies, 1);
+    BOOST_CHECK_EQUAL(v7[2].copies, 1);
+    BOOST_CHECK_EQUAL(v7[3].copies, 0);
+
+    auto v8 = Cat(std::move(v2), std::move(v3));
+    BOOST_CHECK_EQUAL(v8.size(), 3);
+    BOOST_CHECK(v8[0].origin == &t2);
+    BOOST_CHECK(v8[1].origin == &t1);
+    BOOST_CHECK(v8[2].origin == &t2);
+    BOOST_CHECK_EQUAL(v8[0].copies, 0);
+    BOOST_CHECK_EQUAL(v8[1].copies, 1);
+    BOOST_CHECK_EQUAL(v8[2].copies, 0);
+}
+
 BOOST_AUTO_TEST_SUITE_END()

src/txdb.cpp

@@ -13,6 +13,7 @@
 #include <util/system.h>
 #include <ui_interface.h>
 #include <init.h>
+#include <util/vector.h>
 
 #include <stdint.h>
 
@@ -97,7 +98,7 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
     // A vector is used for future extensibility, as we may want to support
     // interrupting after partial writes from multiple independent reorgs.
     batch.Erase(DB_BEST_BLOCK);
-    batch.Write(DB_HEAD_BLOCKS, std::vector<uint256>{hashBlock, old_tip});
+    batch.Write(DB_HEAD_BLOCKS, Vector(hashBlock, old_tip));
 
     for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
         if (it->second.flags & CCoinsCacheEntry::DIRTY) {

src/util/vector.h

@@ -0,0 +1,51 @@
+// Copyright (c) 2019 The Bitcoin 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_VECTOR_H
+#define BITCOIN_UTIL_VECTOR_H
+
+#include <initializer_list>
+#include <type_traits>
+#include <vector>
+
+/** Construct a vector with the specified elements.
+ *
+ * This is preferable over the list initializing constructor of std::vector:
+ * - It automatically infers the element type from its arguments.
+ * - If any arguments are rvalue references, they will be moved into the vector
+ *   (list initialization always copies).
+ */
+template<typename... Args>
+inline std::vector<typename std::common_type<Args...>::type> Vector(Args&&... args)
+{
+    std::vector<typename std::common_type<Args...>::type> ret;
+    ret.reserve(sizeof...(args));
+    // The line below uses the trick from https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
+    (void)std::initializer_list<int>{(ret.emplace_back(std::forward<Args>(args)), 0)...};
+    return ret;
+}
+
+/** Concatenate two vectors, moving elements. */
+template<typename V>
+inline V Cat(V v1, V&& v2)
+{
+    v1.reserve(v1.size() + v2.size());
+    for (auto& arg : v2) {
+        v1.push_back(std::move(arg));
+    }
+    return v1;
+}
+
+/** Concatenate two vectors. */
+template<typename V>
+inline V Cat(V v1, const V& v2)
+{
+    v1.reserve(v1.size() + v2.size());
+    for (const auto& arg : v2) {
+        v1.push_back(arg);
+    }
+    return v1;
+}
+
+#endif // BITCOIN_UTIL_VECTOR_H