mirror of
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78 lines
2.0 KiB
C++
78 lines
2.0 KiB
C++
/*
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Copyright Barrett Adair 2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http ://boost.org/LICENSE_1_0.txt)
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*/
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// NOTE: Due to non-compliance in MSVC, is_constexpr always
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// returns std::false_type on that compiler, which causes
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// the static asserts below to fail.
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#include <type_traits>
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#include <callable_traits/callable_traits.hpp>
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namespace ct = callable_traits;
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//this is a constexpr function object (non-templated)
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struct zero {
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constexpr auto operator()() const {
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return 0;
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}
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};
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static_assert(ct::is_constexpr<zero>(), "");
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static_assert(ct::is_constexpr(zero{}), "");
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//this is a constexpr function object (templated)
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struct subtract {
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// For callable_traits::is_constexpr, generic function objects
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// only need to be SFINAE-friendly if the body of the operator()
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// function accesses member names besides "type" and "value".
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// Unary/binary operators and constructor calls are okay to use.
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template<typename T1, typename T2>
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constexpr auto operator()(T1, T2) const {
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return T1{} - T2{};
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}
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};
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static_assert(ct::is_constexpr<subtract>(), "");
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static_assert(ct::is_constexpr(subtract{}), "");
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//this is NOT a constexpr function object
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struct add {
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template<typename T1, typename T2>
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auto operator()(T1, T2) const {
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return T1{} + T2{};
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}
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};
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static_assert(!ct::is_constexpr<add>(), "");
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static_assert(!ct::is_constexpr(add{}), "");
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/*
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// The case below fails to compile, because lambdas are not trivially
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// default constructible. (Note: This restriction also applies to the
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// argument types). Error message: "Cannot perform constexpr checks
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// with this type, because it is not trivially default constructible."
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auto multiply = [](auto t1, auto t2) -> decltype(t1.value * t2.value) {
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return t1.value * t2.value;
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};
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static_assert(!ct::is_constexpr<decltype(multiply)>(), "");
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static_assert(!ct::is_constexpr(multiply), "");
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*/
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int main() {}
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