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This uses a macro, which can be a bit more brittle than an alias template. However, class template argument deduction for alias templates is only implemented in clang-19.
63 lines
1.6 KiB
C++
63 lines
1.6 KiB
C++
// Copyright (c) 2023 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <span.h>
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#include <boost/test/unit_test.hpp>
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#include <array>
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#include <set>
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#include <vector>
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namespace spannable {
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struct Ignore
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{
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template<typename T> Ignore(T&&) {}
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};
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template<typename T>
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bool Spannable(T&& value, decltype(Span{value})* enable = nullptr)
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{
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return true;
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}
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bool Spannable(Ignore)
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{
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return false;
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}
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struct SpannableYes
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{
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int* data();
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int* begin();
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int* end();
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size_t size();
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};
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struct SpannableNo
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{
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void data();
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size_t size();
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};
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} // namespace spannable
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using namespace spannable;
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BOOST_AUTO_TEST_SUITE(span_tests)
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// Make sure template Span template deduction guides accurately enable calls to
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// Span constructor overloads that work, and disable calls to constructor overloads that
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// don't work. This makes it is possible to use the Span constructor in a SFINAE
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// contexts like in the Spannable function above to detect whether types are or
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// aren't compatible with Spans at compile time.
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BOOST_AUTO_TEST_CASE(span_constructor_sfinae)
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{
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BOOST_CHECK(Spannable(std::vector<int>{}));
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BOOST_CHECK(!Spannable(std::set<int>{}));
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BOOST_CHECK(!Spannable(std::vector<bool>{}));
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BOOST_CHECK(Spannable(std::array<int, 3>{}));
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BOOST_CHECK(Spannable(Span<int>{}));
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BOOST_CHECK(Spannable("char array"));
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BOOST_CHECK(Spannable(SpannableYes{}));
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BOOST_CHECK(!Spannable(SpannableNo{}));
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}
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BOOST_AUTO_TEST_SUITE_END()
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