49 lines
1.8 KiB
C++
49 lines
1.8 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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// REQUIRES: c++11 || c++14 || c++17 || c++20
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// This test makes sure that we don't apply P1951 before C++23, since that is
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// a breaking change. The examples in this test are taken from Richard Smith's
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// comments on https://llvm.org/D109066.
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#include <cassert>
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#include <utility>
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#include <vector>
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struct A {
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int *p_;
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A(int *p) : p_(p) { *p_ += 1; }
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A(const A& a) : p_(a.p_) { *p_ += 1; }
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~A() { *p_ -= 1; }
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};
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int main(int, char**) {
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// Example 1:
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// Without P1951, we call the `pair(int, const A&)` constructor (the converting constructor is not usable because
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// we can't deduce from an initializer list), which creates the A temporary as part of the call to f. With P1951,
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// we call the `pair(U&&, V&&)` constructor, which creates a A temporary inside the pair constructor, and that
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// temporary doesn't live long enough any more.
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{
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int i = 0;
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auto f = [&](std::pair<std::vector<int>, const A&>) { assert(i >= 1); };
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f({{42, 43}, &i});
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}
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// Example 2:
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// Here, n doesn't need to be captured if we call the `pair(const int&, const long&)` constructor, because
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// the lvalue-to-rvalue conversion happens in the lambda. But if we call the `pair(U&&, V&&)` constructor
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// (deducing V = int), then n does need to be captured.
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{
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const int n = 5;
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(void) []{ std::pair<int, long>({1}, n); };
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}
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return 0;
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}
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