a0839b14df
The implementation of tuple's constructors and assignment operators currently diverges from the way the Standard specifies them, which leads to subtle cases where the behavior is not as specified. In particular, a class derived from a tuple-like type (e.g. pair) can't be assigned to a tuple with corresponding members, when it should. This commit re-implements the assignment operators (BUT NOT THE CONSTRUCTORS) in a way much closer to the specification to get rid of this bug. Most of the tests have been stolen from Eric's patch https://reviews.llvm.org/D27606. As a fly-by improvement, tests for noexcept correctness have been added to all overloads of operator=. We should tackle the same issue for the tuple constructors in a future patch - I'm just trying to make progress on fixing this long-standing bug. PR17550 rdar://15837420 Differential Revision: https://reviews.llvm.org/D50106
78 lines
2.1 KiB
C++
78 lines
2.1 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03
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// This test ensures that std::tuple is lazy when it comes to checking whether
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// the elements it is assigned from can be used to assign to the types in
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// the tuple.
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#include <tuple>
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#include <array>
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template <bool Enable, class ...Class>
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constexpr typename std::enable_if<Enable, bool>::type BlowUp() {
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static_assert(Enable && sizeof...(Class) != sizeof...(Class), "");
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return true;
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}
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template<class T>
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struct Fail {
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static_assert(sizeof(T) != sizeof(T), "");
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using type = void;
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};
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struct NoAssign {
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NoAssign() = default;
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NoAssign(NoAssign const&) = default;
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template <class T, class = typename std::enable_if<sizeof(T) != sizeof(T)>::type>
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NoAssign& operator=(T) { return *this; }
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};
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template <int>
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struct DieOnAssign {
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DieOnAssign() = default;
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template <class T, class X = typename std::enable_if<!std::is_same<T, DieOnAssign>::value>::type,
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class = typename Fail<X>::type>
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DieOnAssign& operator=(T) {
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return *this;
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}
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};
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void test_arity_checks() {
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{
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using T = std::tuple<int, DieOnAssign<0>, int>;
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using P = std::pair<int, int>;
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static_assert(!std::is_assignable<T&, P const&>::value, "");
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}
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{
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using T = std::tuple<int, int, DieOnAssign<1> >;
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using A = std::array<int, 1>;
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static_assert(!std::is_assignable<T&, A const&>::value, "");
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}
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}
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void test_assignability_checks() {
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{
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using T1 = std::tuple<int, NoAssign, DieOnAssign<2> >;
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using T2 = std::tuple<long, long, long>;
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static_assert(!std::is_assignable<T1&, T2 const&>::value, "");
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}
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{
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using T1 = std::tuple<NoAssign, DieOnAssign<3> >;
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using T2 = std::pair<long, double>;
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static_assert(!std::is_assignable<T1&, T2 const&>::value, "");
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}
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}
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int main(int, char**) {
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test_arity_checks();
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test_assignability_checks();
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return 0;
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}
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