Add util::Ref class as temporary alternative for c++17 std::any

This commit does not change behavior

5 files changed, 77 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 13812de0e7..d2c7400bbb 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -223,6 +223,7 @@ BITCOIN_CORE_H = \
   util/message.h \
   util/moneystr.h \
   util/rbf.h \
+  util/ref.h \
   util/settings.h \
   util/string.h \
   util/threadnames.h \
diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 3a0d4fdc15..6ba0e9f270 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -229,6 +229,7 @@ BITCOIN_TESTS =\
   test/prevector_tests.cpp \
   test/raii_event_tests.cpp \
   test/random_tests.cpp \
+  test/ref_tests.cpp \
   test/reverselock_tests.cpp \
   test/rpc_tests.cpp \
   test/sanity_tests.cpp \
diff --git a/src/test/ref_tests.cpp b/src/test/ref_tests.cpp
new file mode 100644
index 0000000000..0ec0799fbc
--- /dev/null
+++ b/src/test/ref_tests.cpp
@@ -0,0 +1,33 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/ref.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_SUITE(ref_tests)
+
+BOOST_AUTO_TEST_CASE(ref_test)
+{
+    util::Ref ref;
+    BOOST_CHECK(!ref.Has<int>());
+    BOOST_CHECK_THROW(ref.Get<int>(), NonFatalCheckError);
+    int value = 5;
+    ref.Set(value);
+    BOOST_CHECK(ref.Has<int>());
+    BOOST_CHECK_EQUAL(ref.Get<int>(), 5);
+    ++ref.Get<int>();
+    BOOST_CHECK_EQUAL(ref.Get<int>(), 6);
+    BOOST_CHECK_EQUAL(value, 6);
+    ++value;
+    BOOST_CHECK_EQUAL(value, 7);
+    BOOST_CHECK_EQUAL(ref.Get<int>(), 7);
+    BOOST_CHECK(!ref.Has<bool>());
+    BOOST_CHECK_THROW(ref.Get<bool>(), NonFatalCheckError);
+    ref.Clear();
+    BOOST_CHECK(!ref.Has<int>());
+    BOOST_CHECK_THROW(ref.Get<int>(), NonFatalCheckError);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/util/check.h b/src/util/check.h
index d18887ae95..5c0f32cf51 100644
--- a/src/util/check.h
+++ b/src/util/check.h
@@ -5,6 +5,10 @@
 #ifndef BITCOIN_UTIL_CHECK_H
 #define BITCOIN_UTIL_CHECK_H
 
+#if defined(HAVE_CONFIG_H)
+#include <config/bitcoin-config.h>
+#endif
+
 #include <tinyformat.h>
 
 #include <stdexcept>
diff --git a/src/util/ref.h b/src/util/ref.h
new file mode 100644
index 0000000000..9685ea9fec
--- /dev/null
+++ b/src/util/ref.h
@@ -0,0 +1,38 @@
+// Copyright (c) 2020 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_REF_H
+#define BITCOIN_UTIL_REF_H
+
+#include <util/check.h>
+
+#include <typeindex>
+
+namespace util {
+
+/**
+ * Type-safe dynamic reference.
+ *
+ * This implements a small subset of the functionality in C++17's std::any
+ * class, and can be dropped when the project updates to C++17
+ * (https://github.com/bitcoin/bitcoin/issues/16684)
+ */
+class Ref
+{
+public:
+    Ref() = default;
+    template<typename T> Ref(T& value) { Set(value); }
+    template<typename T> T& Get() const { CHECK_NONFATAL(Has<T>()); return *static_cast<T*>(m_value); }
+    template<typename T> void Set(T& value) { m_value = &value; m_type = std::type_index(typeid(T)); }
+    template<typename T> bool Has() const { return m_value && m_type == std::type_index(typeid(T)); }
+    void Clear() { m_value = nullptr; m_type = std::type_index(typeid(void)); }
+
+private:
+    void* m_value = nullptr;
+    std::type_index m_type = std::type_index(typeid(void));
+};
+
+} // namespace util
+
+#endif // BITCOIN_UTIL_REF_H