add variant class with cleaner interface than boost::variant<>

4 files changed, 575 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index b712ee6b1..189207fad 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -81,6 +81,9 @@ target_link_libraries(common
   PRIVATE
     ${OPENSSL_LIBRARIES}
     ${EXTRA_LIBRARIES})
+target_include_directories(common
+  PRIVATE
+    ${Boost_INCLUDE_DIRS})
 
 #monero_install_headers(common
 #  ${common_headers})
diff --git a/src/common/variant.h b/src/common/variant.h
new file mode 100644
index 000000000..a2121c75e
--- /dev/null
+++ b/src/common/variant.h
@@ -0,0 +1,156 @@
+// Copyright (c) 2022, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Variant wrapper class.
+
+#pragma once
+
+//local headers
+
+//third party headers
+#include <boost/blank.hpp>
+#include <boost/mpl/begin_end.hpp>
+#include <boost/mpl/distance.hpp>
+#include <boost/mpl/find.hpp>
+#include <boost/mpl/vector.hpp>
+#include <boost/none_t.hpp>
+#include <boost/variant/apply_visitor.hpp>
+#include <boost/variant/get.hpp>
+#include <boost/variant/static_visitor.hpp>
+#include <boost/variant/variant.hpp>
+
+//standard headers
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+
+//forward declarations
+
+
+namespace tools
+{
+
+[[noreturn]] inline void variant_static_visitor_blank_err()
+{ throw std::runtime_error("variant: tried to visit an empty variant."); }
+[[noreturn]] inline void variant_unwrap_err()
+{ throw std::runtime_error("variant: tried to access value of incorrect type."); }
+
+////
+// variant: convenience wrapper around boost::variant with a cleaner interface
+// - the value may be assigned to but is otherwise read-only
+// - the variant is 'optional' - an empty variant will evaluate to 'false' and an initialized variant will be 'true'
+///
+template <typename ResultT>
+struct variant_static_visitor : public boost::static_visitor<ResultT>
+{
+    /// provide visitation for empty variants
+    /// - add this to your visitor with: using variant_static_visitor::operator();
+    [[noreturn]] ResultT operator()(const boost::blank) const { variant_static_visitor_blank_err(); }
+};
+
+template <typename... Types>
+class variant final
+{
+    using VType = boost::variant<boost::blank, Types...>;
+
+public:
+//constructors
+    /// default constructor
+    variant() = default;
+    variant(boost::none_t) : variant{} {}  //act like boost::optional
+
+    /// construct from variant type (use enable_if to avoid issues with copy/move constructor)
+    template <typename T,
+        typename std::enable_if<
+                !std::is_same<
+                        std::remove_cv_t<std::remove_reference_t<T>>,
+                        variant<Types...>
+                    >::value,
+                bool
+            >::type = true>
+    variant(T &&value) : m_value{std::forward<T>(value)} {}
+
+//overloaded operators
+    /// boolean operator: true if the variant isn't empty/uninitialized
+    explicit operator bool() const noexcept { return !this->is_empty(); }
+
+//member functions
+    /// check if empty/uninitialized
+    bool is_empty() const noexcept { return m_value.which() == 0; }
+
+    /// check the variant type
+    template <typename T>
+    bool is_type() const noexcept { return this->index() == this->type_index_of<T>(); }
+
+    /// try to get a read-only handle to the embedded value (return nullptr on failure)
+    template <typename T>
+    const T* try_unwrap() const
+    {
+        return boost::strict_get<T>(&m_value);
+    }
+
+    /// get a read-only handle to the embedded value
+    template <typename T>
+    const T& unwrap() const
+    {
+        const T *value_ptr{this->try_unwrap<T>()};
+        if (!value_ptr) variant_unwrap_err();
+        return *value_ptr;
+    }
+
+    /// get the type index of the currently stored type
+    int index() const noexcept { return m_value.which(); }
+
+    /// get the type index of a requested type (compile error for invalid types) (boost::mp11 is boost 1.66.0)
+    template <typename T>
+    static constexpr int type_index_of() noexcept
+    {
+        using types = boost::mpl::vector<boost::blank, Types...>;
+        using elem = typename boost::mpl::find<types, T>::type;
+        using begin = typename boost::mpl::begin<types>::type;
+        return boost::mpl::distance<begin, elem>::value;
+    }
+
+    /// check if two variants have the same type
+    static bool same_type(const variant<Types...> &v1, const variant<Types...> &v2) noexcept
+    { return v1.index() == v2.index(); }
+
+    /// apply a visitor to the variant
+    template <typename VisitorT>
+    typename VisitorT::result_type visit(VisitorT &&visitor) const
+    {
+        return boost::apply_visitor(std::forward<VisitorT>(visitor), m_value);
+    }
+
+private:
+//member variables
+    /// variant of all value types
+    VType m_value;
+};
+
+} //namespace tools
diff --git a/tests/unit_tests/CMakeLists.txt b/tests/unit_tests/CMakeLists.txt
index 55818dc93..835567953 100644
--- a/tests/unit_tests/CMakeLists.txt
+++ b/tests/unit_tests/CMakeLists.txt
@@ -90,6 +90,7 @@ set(unit_tests_sources
   hardfork.cpp
   unbound.cpp
   uri.cpp
+  variant.cpp
   varint.cpp
   ringct.cpp
   output_selection.cpp
diff --git a/tests/unit_tests/variant.cpp b/tests/unit_tests/variant.cpp
new file mode 100644
index 000000000..c22200a8c
--- /dev/null
+++ b/tests/unit_tests/variant.cpp
@@ -0,0 +1,415 @@
+// Copyright (c) 2023, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "common/variant.h"
+
+#include <boost/mpl/deref.hpp>
+#include <boost/variant/recursive_wrapper.hpp>
+#include <boost/variant/recursive_variant.hpp>
+
+#include "gtest/gtest.h"
+
+#include <sstream>
+#include <type_traits>
+#include <vector>
+
+using tools::variant;
+using tools::variant_static_visitor;
+
+namespace
+{
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template <typename T>
+using strip_all_t = std::remove_reference_t<std::remove_cv_t<T>>;
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template <typename T, typename U>
+using strip_same = std::is_same<strip_all_t<T>, strip_all_t<U>>;
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    typename PositiveType,
+    typename TestType,
+    typename... VariantTypes,
+    class VecTypes         = boost::mpl::vector<VariantTypes...>,
+    class VecBegin         = typename boost::mpl::begin<VecTypes>::type,
+    class VecIndexT        = typename boost::mpl::find<VecTypes, TestType>::type,
+    size_t TYPE_INDEX      = boost::mpl::distance<VecBegin, VecIndexT>::value,
+    bool LAST_VARIANT_TYPE = TYPE_INDEX == sizeof...(VariantTypes) - 1
+>
+static std::enable_if_t<LAST_VARIANT_TYPE>
+test_is_type_match(const variant<VariantTypes...>& v)
+{
+    constexpr bool expected = strip_same<PositiveType, TestType>();
+    const bool actual = v.template is_type<TestType>();
+    EXPECT_EQ(expected, actual);
+
+    EXPECT_FALSE(v.template is_type<boost::blank>());
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    typename PositiveType,
+    typename TestType,
+    typename... VariantTypes,
+    class VecTypes         = boost::mpl::vector<VariantTypes...>,
+    class VecBegin         = typename boost::mpl::begin<VecTypes>::type,
+    class VecIndexT        = typename boost::mpl::find<VecTypes, TestType>::type,
+    size_t TYPE_INDEX      = boost::mpl::distance<VecBegin, VecIndexT>::value,
+    bool LAST_VARIANT_TYPE = TYPE_INDEX == sizeof...(VariantTypes) - 1
+>
+static std::enable_if_t<!LAST_VARIANT_TYPE>
+test_is_type_match(const variant<VariantTypes...>& v)
+{
+    constexpr bool expected = strip_same<PositiveType, TestType>();
+    const bool actual = v.template is_type<TestType>();
+    EXPECT_EQ(expected, actual);
+
+    using NextTypeIt   = typename boost::mpl::advance<VecIndexT, boost::mpl::int_<1>>::type;
+    using NextTestType = typename boost::mpl::deref<NextTypeIt>::type;
+    test_is_type_match<PositiveType, NextTestType>(v);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    typename VariantType0,
+    typename... VariantTypesRest,
+    typename AssignType
+>
+static void test_is_type_ref
+(
+    variant<VariantType0, VariantTypesRest...>& v,
+    AssignType&& val
+)
+{
+    v = val;
+    test_is_type_match<AssignType, VariantType0>(v);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    typename VariantType0,
+    typename... VariantTypesRest,
+    typename AssignType0,
+    typename... AssignTypesRest
+>
+static void test_is_type_ref
+(
+    variant<VariantType0, VariantTypesRest...>& v,
+    AssignType0&& val_0,
+    AssignTypesRest&&... val_rest
+)
+{
+    v = val_0;
+    test_is_type_match<AssignType0, VariantType0>(v);
+    test_is_type_ref(v, val_rest...);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template <typename... VariantTypes>
+static void test_is_type_full(VariantTypes&&... test_vals)
+{
+    variant<VariantTypes...> v;
+    test_is_type_ref(v, test_vals...);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    size_t IJ = 0,
+    typename... VariantTypes,
+    bool END = IJ == sizeof...(VariantTypes) * sizeof...(VariantTypes)
+>
+static std::enable_if_t<END>
+test_same_type_ref
+(
+    variant<VariantTypes...>& v1,
+    variant<VariantTypes...>& v2,
+    const std::tuple<VariantTypes...>& tup_i,
+    const std::tuple<VariantTypes...>& tup_j
+)
+{ /* trivial end case */ }
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template
+<
+    size_t IJ = 0,
+    typename... VariantTypes,
+    bool END = IJ == sizeof...(VariantTypes) * sizeof...(VariantTypes)
+>
+static std::enable_if_t<!END>
+test_same_type_ref
+(
+    variant<VariantTypes...>& v1,
+    variant<VariantTypes...>& v2,
+    const std::tuple<VariantTypes...>& tup_i,
+    const std::tuple<VariantTypes...>& tup_j
+)
+{
+    constexpr size_t I = IJ / sizeof...(VariantTypes);
+    constexpr size_t J = IJ % sizeof...(VariantTypes);
+    constexpr bool expected = I == J;
+
+    v1 = std::get<I>(tup_i);
+    v2 = std::get<J>(tup_j);
+    const bool actual = variant<VariantTypes...>::same_type(v1, v2);
+
+    EXPECT_EQ(expected, actual);
+
+    test_same_type_ref<IJ + 1>(v1, v2, tup_i, tup_j);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+template <typename... VariantTypes>
+static void test_same_type_full
+(
+    const std::tuple<VariantTypes...>& vals_i,
+    const std::tuple<VariantTypes...>& vals_j
+)
+{
+    using Variant = variant<VariantTypes...>;
+    Variant v_i;
+    Variant v_j;
+    test_same_type_ref(v_i, v_j, vals_i, vals_j);
+}
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+struct test_stringify_visitor: public variant_static_visitor<std::string>
+{
+    template <typename T>
+    static std::string stringify(const T& t)
+    {
+        std::stringstream ss;
+        ss << typeid(T).name();
+        ss << "::";
+        ss << t;
+        return ss.str();
+    }
+
+    template <class Variant, typename T>
+    static void test_visitation(const Variant& v, const T& t)
+    {
+        EXPECT_EQ(test_stringify_visitor::stringify(t), v.visit(test_stringify_visitor()));
+    }
+
+    // Make sure boost::blank errors
+    using variant_static_visitor::operator();
+
+    // Visitation implementation
+    template <typename T>
+    std::string operator()(const T& t) const
+    {
+        return test_stringify_visitor::stringify(t);
+    }
+};
+} // anonymous namespace
+//-------------------------------------------------------------------------------------------------------------------
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, operatorbool)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_FALSE(v);
+    v = (int16_t) 2023;
+    EXPECT_TRUE(v);
+    v = (int16_t) 0;
+    EXPECT_TRUE(v);
+    v = boost::blank{};
+    EXPECT_FALSE(v);
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, is_empty)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_TRUE(v.is_empty());
+    v = (int16_t) 2023;
+    EXPECT_FALSE(v.is_empty());
+    v = (int16_t) 0;
+    EXPECT_FALSE(v.is_empty());
+    v = boost::blank{};
+    EXPECT_TRUE(v.is_empty());
+
+    variant<> v2;
+    EXPECT_TRUE(v2.is_empty());
+    v2 = boost::blank{};
+    EXPECT_TRUE(v2.is_empty());
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, is_type)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_TRUE(v.is_type<boost::blank>());
+    v = (int16_t) 2023;
+    EXPECT_TRUE(v.is_type<int16_t>());
+
+    test_is_type_full((uint32_t) 2023, (char) '\n', std::string("HOWDY"));
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, try_unwrap)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_FALSE(v.try_unwrap<int8_t>());
+    v = (int16_t) 5252;
+    ASSERT_TRUE(v.try_unwrap<int16_t>());
+    EXPECT_EQ(5252, *v.try_unwrap<int16_t>());
+    EXPECT_FALSE(v.try_unwrap<uint16_t>());
+    EXPECT_FALSE(v.try_unwrap<std::string>());
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, unwrap)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_THROW(v.unwrap<int8_t>(), std::runtime_error);
+    v = (int16_t) 5252;
+    EXPECT_EQ(5252, v.unwrap<int16_t>());
+    EXPECT_THROW(v.unwrap<uint16_t>(), std::runtime_error);
+    EXPECT_THROW(v.unwrap<std::string>(), std::runtime_error);
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, index)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_EQ(0, v.index());
+    v = (int8_t) 7;
+    EXPECT_EQ(1, v.index());
+    v = (uint8_t) 7;
+    EXPECT_EQ(2, v.index());
+    v = (int16_t) 7;
+    EXPECT_EQ(3, v.index());
+    v = (uint16_t) 7;
+    EXPECT_EQ(4, v.index());
+    v = "verifiable variant vying for vengence versus visa";
+    EXPECT_EQ(5, v.index());
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, type_index_of)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_EQ(0, decltype(v)::type_index_of<boost::blank>());
+    EXPECT_EQ(1, decltype(v)::type_index_of<int8_t>());
+    EXPECT_EQ(2, decltype(v)::type_index_of<uint8_t>());
+    EXPECT_EQ(3, decltype(v)::type_index_of<int16_t>());
+    EXPECT_EQ(4, decltype(v)::type_index_of<uint16_t>());
+    EXPECT_EQ(5, decltype(v)::type_index_of<std::string>());
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, constexpr_type_index_of)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    constexpr int TINDEX0 = decltype(v)::type_index_of<boost::blank>();
+    EXPECT_EQ(0, TINDEX0);
+    constexpr int TINDEX5 = decltype(v)::type_index_of<std::string>();
+    EXPECT_EQ(5, TINDEX5);
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, same_type)
+{
+    const std::tuple<int, std::string, char> vals_i(77840, "Hullubaloo", '\0');
+    const std::tuple<int, std::string, char> vals_j(1876, "Canneck", '\t');
+    test_same_type_full(vals_i, vals_j);
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, visit)
+{
+    variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
+    EXPECT_THROW(v.visit(test_stringify_visitor()), std::runtime_error);
+
+    v = "Rev";
+    test_stringify_visitor::test_visitation(v, std::string("Rev"));
+
+    v = (int16_t) 2001;
+    test_stringify_visitor::test_visitation(v, (int16_t) 2001);
+    EXPECT_NE(test_stringify_visitor::stringify((uint16_t) 2001), v.visit(test_stringify_visitor()));
+}
+//-------------------------------------------------------------------------------------------------------------------
+TEST(variant, ad_hoc_recursion)
+{
+    struct left_t;
+    struct right_t;
+
+    using twisty = variant<boost::recursive_wrapper<left_t>, boost::recursive_wrapper<right_t>>;
+
+    struct left_t
+    {
+        twisty l;
+    };
+
+    struct right_t
+    {
+        twisty r;
+    };
+
+    auto right = [](twisty&& t = {}) -> twisty
+    {
+        right_t r;
+        r.r = t;
+        return r;
+    };
+
+    auto left = [](twisty&& t = {}) -> twisty
+    {
+        left_t l;
+        l.l = t;
+        return l;
+    };
+
+    struct twisty_counter: variant_static_visitor<std::pair<int, int>>
+    {
+        std::pair<int, int> operator()(boost::blank) const
+        {
+            return {0, 0};
+        }
+
+        std::pair<int, int> operator()(const left_t& l) const
+        {
+            auto count = l.l.visit(twisty_counter());
+            count.first += 1;
+            return count;
+        }
+
+        std::pair<int, int> operator()(const right_t& r) const
+        {
+            auto count = r.r.visit(twisty_counter());
+            count.second += 1;
+            return count;
+        }
+    };
+
+    const twisty tw = left(left(right(right(left(right(left(right(left()))))))));
+
+    int left_count, right_count;
+    std::tie(left_count, right_count) = tw.visit(twisty_counter());
+
+    EXPECT_EQ(5, left_count);
+    EXPECT_EQ(4, right_count);
+}
+//-------------------------------------------------------------------------------------------------------------------