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Framework: helper to decompose structs to tuples
This should come handy, among other things, for the AnalysisTask business.
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‎Framework/Foundation/CMakeLists.txt‎

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@@ -14,3 +14,8 @@ o2_add_test(test_Traits NAME test_FrameworkFoundation_test_Traits
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COMPONENT_NAME FrameworkFoundation
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SOURCES test/test_Traits.cxx
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PUBLIC_LINK_LIBRARIES O2::FrameworkFoundation)
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o2_add_test(test_StructToTuple NAME test_FrameworkFoundation_StructToTuple
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COMPONENT_NAME FrameworkFoundation
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SOURCES test/test_StructToTuple.cxx
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PUBLIC_LINK_LIBRARIES O2::FrameworkFoundation)

‎Framework/Foundation/include/Framework/StructToTuple.h‎

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// Copyright CERN and copyright holders of ALICE O2. This software is
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// distributed under the terms of the GNU General Public License v3 (GPL
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// Version 3), copied verbatim in the file "COPYING".
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//
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// See http://alice-o2.web.cern.ch/license for full licensing information.
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//
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// In applying this license CERN does not waive the privileges and immunities
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// granted to it by virtue of its status as an Intergovernmental Organization
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// or submit itself to any jurisdiction.
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#include <Framework/Traits.h>
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#include <tuple>
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#include <type_traits>
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namespace o2::framework
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{
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struct any_type {
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template <class T>
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constexpr operator T(); // non explicit
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};
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template <class T, typename... Args>
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decltype(void(T{ std::declval<Args>()... }), std::true_type())
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test(int);
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template <class T, typename... Args>
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std::false_type
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test(...);
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template <class T, typename... Args>
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struct is_braces_constructible : decltype(test<T, Args...>(0)) {
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};
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/// Helper function to convert a brace-initialisable struct to
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/// a tuple.
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template <class T>
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auto constexpr to_tuple(T&& object) noexcept
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{
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using type = std::decay_t<T>;
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if constexpr (is_braces_constructible<type, any_type, any_type, any_type, any_type>{}) {
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auto&& [p1, p2, p3] = object;
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return std::make_tuple(p1, p2, p3);
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} else if constexpr (is_braces_constructible<type, any_type, any_type, any_type>{}) {
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auto&& [p1, p2] = object;
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return std::make_tuple(p1, p2);
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} else if constexpr (is_braces_constructible<type, any_type, any_type>{}) {
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auto&& [p1] = object;
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return std::make_tuple(p1);
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} else if constexpr (is_braces_constructible<type, any_type>{}) {
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return std::make_tuple();
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} else {
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static_assert(always_static_assert<type>(), "You must inherit from AnalysisTask");
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}
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}
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/// Helper function to convert a brace-initialisable struct to
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/// a tuple.
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template <class T>
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auto constexpr to_tuple_refs(T&& object) noexcept
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{
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using type = std::decay_t<T>;
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if constexpr (is_braces_constructible<type, any_type, any_type, any_type, any_type>{}) {
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auto&& [p1, p2, p3] = object;
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return std::tie(p1, p2, p3);
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} else if constexpr (is_braces_constructible<type, any_type, any_type, any_type>{}) {
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auto&& [p1, p2] = object;
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return std::tie(p1, p2);
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} else if constexpr (is_braces_constructible<type, any_type, any_type>{}) {
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auto&& [p1] = object;
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return std::tie(p1);
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} else if constexpr (is_braces_constructible<type, any_type>{}) {
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return std::make_tuple();
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} else {
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static_assert(always_static_assert<type>(), "You must inherit from AnalysisTask");
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}
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}
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} // namespace o2::framework

‎Framework/Foundation/test/test_StructToTuple.cxx‎

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// Copyright CERN and copyright holders of ALICE O2. This software is
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// distributed under the terms of the GNU General Public License v3 (GPL
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// Version 3), copied verbatim in the file "COPYING".
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//
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// See http://alice-o2.web.cern.ch/license for full licensing information.
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//
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// In applying this license CERN does not waive the privileges and immunities
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// granted to it by virtue of its status as an Intergovernmental Organization
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// or submit itself to any jurisdiction.
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#define BOOST_TEST_MODULE Test Framework Traits
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#define BOOST_TEST_MAIN
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#define BOOST_TEST_DYN_LINK
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#include <boost/test/unit_test.hpp>
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#include "Framework/StructToTuple.h"
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struct Foo {
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};
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// FIXME: this should really struct Bar : Foo, but a c++17 bug
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// in GCC 7.3 (solved in 7.4 / 8.x) prevents us from doing so
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// for now.
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struct Bar : Foo {
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int foo = 1;
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int bar = 2;
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};
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BOOST_AUTO_TEST_CASE(TestStructToTuple)
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{
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Foo foo;
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//auto t1 = o2::framework::to_tuple(foo);
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//#BOOST_CHECK_EQUAL(std::get<0>(t1), 1);
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// Expand a struct which inherits from
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// another..
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Bar bar{ {}, 4, 5 };
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BOOST_CHECK_EQUAL(bar.foo, 4);
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BOOST_CHECK_EQUAL(bar.bar, 5);
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auto t2 = o2::framework::to_tuple(bar);
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BOOST_CHECK_EQUAL(std::get<0>(t2), 4);
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BOOST_CHECK_EQUAL(std::get<1>(t2), 5);
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std::get<0>(t2) = 10;
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BOOST_CHECK_EQUAL(std::get<0>(t2), 10);
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BOOST_CHECK_EQUAL(bar.foo, 4);
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auto t3 = o2::framework::to_tuple_refs(bar);
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BOOST_CHECK_EQUAL(std::get<0>(t3), 4);
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BOOST_CHECK_EQUAL(std::get<1>(t3), 5);
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std::get<0>(t3) = 10;
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BOOST_CHECK_EQUAL(std::get<0>(t3), 10);
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BOOST_CHECK_EQUAL(bar.foo, 10);
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}

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