49 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// REQUIRES: c++11 || c++14 || c++17 || c++2010 11// This test makes sure that we don't apply P1951 before C++23, since that is12// a breaking change. The examples in this test are taken from Richard Smith's13// comments on https://llvm.org/D109066.14 15#include <cassert>16#include <utility>17#include <vector>18 19struct A {20 int *p_;21 A(int *p) : p_(p) { *p_ += 1; }22 A(const A& a) : p_(a.p_) { *p_ += 1; }23 ~A() { *p_ -= 1; }24};25 26int main(int, char**) {27 // Example 1:28 // Without P1951, we call the `pair(int, const A&)` constructor (the converting constructor is not usable because29 // we can't deduce from an initializer list), which creates the A temporary as part of the call to f. With P1951,30 // we call the `pair(U&&, V&&)` constructor, which creates a A temporary inside the pair constructor, and that31 // temporary doesn't live long enough any more.32 {33 int i = 0;34 auto f = [&](std::pair<std::vector<int>, const A&>) { assert(i >= 1); };35 f({{42, 43}, &i});36 }37 38 // Example 2:39 // Here, n doesn't need to be captured if we call the `pair(const int&, const long&)` constructor, because40 // the lvalue-to-rvalue conversion happens in the lambda. But if we call the `pair(U&&, V&&)` constructor41 // (deducing V = int), then n does need to be captured.42 {43 const int n = 5;44 (void) []{ std::pair<int, long>({1}, n); };45 }46 47 return 0;48}49