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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// REQUIRES: std-at-least-c++26
// <optional>
// constexpr iterator optional::begin() noexcept;
// constexpr const_iterator optional::begin() const noexcept;
#include <cassert>
#include <iterator>
#include <optional>
#include <type_traits>
#include <utility>
template <typename T>
constexpr bool test() {
std::optional<T> opt{T{}};
{ // begin() is marked noexcept
static_assert(noexcept(opt.begin()));
static_assert(noexcept(std::as_const(opt).begin()));
}
{ // Dereferencing an iterator at the beginning == indexing the 0th element, and that calling begin() again return the same iterator.
auto iter1 = opt.begin();
auto iter2 = std::as_const(opt).begin();
assert(*iter1 == iter1[0]);
assert(*iter2 == iter2[0]);
assert(iter1 == opt.begin());
assert(iter2 == std::as_const(opt).begin());
}
{ // Calling begin() multiple times on a disengaged optional returns the same iterator.
std::optional<T> disengaged{std::nullopt};
auto iter1 = disengaged.begin();
auto iter2 = std::as_const(disengaged).begin();
assert(iter1 == disengaged.begin());
assert(iter2 == std::as_const(disengaged).begin());
}
return true;
}
constexpr bool tests() {
assert(test<int>());
assert(test<char>());
assert(test<const int>());
assert(test<const char>());
return true;
}
int main(int, char**) {
assert(tests());
static_assert(tests());
return 0;
}
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