166 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// <utility>10 11// template <class T1, class T2> struct pair12 13// Test the SFINAE required by LWG Issue #2367.14// is_default_constructible<pair>15 16// UNSUPPORTED: c++0317 18#include <utility>19#include <type_traits>20#include <cassert>21 22#include "test_macros.h"23 24#if TEST_STD_VER > 1125#define CONSTEXPR_CXX14 constexpr26#define STATIC_ASSERT_CXX14(Pred) static_assert(Pred, "")27#else28#define CONSTEXPR_CXX1429#define STATIC_ASSERT_CXX14(Pred) assert(Pred)30#endif31 32struct DeletedDefault {33 // A class with a deleted default constructor. Used to test the SFINAE34 // on std::pair's default constructor.35 constexpr explicit DeletedDefault(int x) : value(x) {}36 constexpr DeletedDefault() = delete;37 int value;38};39 40template <class Tp, bool>41struct DependantType: public Tp {};42 43template <class T, bool Val>44using DependantIsDefault = DependantType<std::is_default_constructible<T>, Val>;45 46template <class T>47struct DefaultSFINAES {48 template <bool Dummy = false, class = typename std::enable_if<49 DependantIsDefault<T, Dummy>::value50 >::type51 >52 constexpr DefaultSFINAES() : value() {}53 constexpr explicit DefaultSFINAES(T const& x) : value(x) {}54 T value;55};56 57struct NoDefault {58 constexpr NoDefault(int v) : value(v) {}59 int value;60};61 62template <class Tp>63void test_not_is_default_constructible()64{65 {66 typedef std::pair<int, Tp> P;67 static_assert(!std::is_default_constructible<P>::value, "");68 static_assert(std::is_constructible<P, int, Tp>::value, "");69 }70 {71 typedef std::pair<Tp, int> P;72 static_assert(!std::is_default_constructible<P>::value, "");73 static_assert(std::is_constructible<P, Tp, int>::value, "");74 }75 {76 typedef std::pair<Tp, Tp> P;77 static_assert(!std::is_default_constructible<P>::value, "");78 static_assert(std::is_constructible<P, Tp, Tp>::value, "");79 }80}81 82template <class Tp>83void test_is_default_constructible()84{85 {86 typedef std::pair<int, Tp> P;87 static_assert(std::is_default_constructible<P>::value, "");88 }89 {90 typedef std::pair<Tp, int> P;91 static_assert(std::is_default_constructible<P>::value, "");92 }93 {94 typedef std::pair<Tp, Tp> P;95 static_assert(std::is_default_constructible<P>::value, "");96 }97}98 99template <class T>100struct IllFormedDefaultImp {101 constexpr explicit IllFormedDefaultImp(int v) : value(v) {}102 constexpr IllFormedDefaultImp() : value(T::DoesNotExistAndShouldNotCompile) {}103 int value;104};105 106typedef IllFormedDefaultImp<int> IllFormedDefault;107 // A class which provides a constexpr default constructor with a valid108 // signature but an ill-formed body. The A compile error will be emitted if109 // the default constructor is instantiated.110 111 112// Check that the SFINAE on the default constructor is not evaluated when113// it isn't needed. If the default constructor of 'IllFormedDefault' is evaluated114// in C++11, even with is_default_constructible, then this test should fail to115// compile. In C++14 and greater evaluate each test is evaluated as a constant116// expression.117// See LWG issue #2367118void test_illformed_default()119{120 {121 typedef std::pair<IllFormedDefault, int> P;122 static_assert((std::is_constructible<P, IllFormedDefault, int>::value), "");123 CONSTEXPR_CXX14 P p(IllFormedDefault(42), -5);124 STATIC_ASSERT_CXX14(p.first.value == 42 && p.second == -5);125 }126 {127 typedef std::pair<int, IllFormedDefault> P;128 static_assert((std::is_constructible<P, int, IllFormedDefault>::value), "");129 CONSTEXPR_CXX14 IllFormedDefault dd(-5);130 CONSTEXPR_CXX14 P p(42, dd);131 STATIC_ASSERT_CXX14(p.first == 42 && p.second.value == -5);132 }133 {134 typedef std::pair<IllFormedDefault, IllFormedDefault> P;135 static_assert((std::is_constructible<P, IllFormedDefault, IllFormedDefault>::value), "");136 CONSTEXPR_CXX14 P p(IllFormedDefault(42), IllFormedDefault(-5));137 STATIC_ASSERT_CXX14(p.first.value == 42 && p.second.value == -5);138 }139}140 141 142int main(int, char**)143{144 {145 // Check that pair<T, U> can still be used even if146 // is_default_constructible<T> or is_default_constructible<U> cause147 // a compilation error.148 test_illformed_default();149 }150 {151 // pair::pair() is only disable in C++11 and beyond.152 test_not_is_default_constructible<NoDefault>();153 test_not_is_default_constructible<DeletedDefault>();154 test_not_is_default_constructible<DefaultSFINAES<int&>>();155 test_not_is_default_constructible<DefaultSFINAES<int&&>>();156 test_not_is_default_constructible<int&>();157 test_not_is_default_constructible<int&&>();158 }159 {160 test_is_default_constructible<int>();161 test_is_default_constructible<DefaultSFINAES<int>>();162 }163 164 return 0;165}166