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clang-p2996/libcxx/test/std/containers/container.adaptors/flat.multiset/flat.multiset.cons/deduct.compile.pass.cpp

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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
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
// <flat_set>
// Test CTAD on cases where deduction should fail.
#include <flat_set>
#include <functional>
#include <memory>
#include <utility>
#include <vector>
struct NotAnAllocator {
friend bool operator<(NotAnAllocator, NotAnAllocator) { return false; }
};
template <class... Args>
concept CanDeductFlatMultiSet = requires { std::flat_multiset(std::declval<Args>()...); };
static_assert(CanDeductFlatMultiSet<std::vector<int>>);
// cannot deduce Key and T from nothing
static_assert(!CanDeductFlatMultiSet<>);
// cannot deduce Key and T from just (Compare)
static_assert(!CanDeductFlatMultiSet<std::less<int>>);
// cannot deduce Key and T from just (Compare, Allocator)
static_assert(!CanDeductFlatMultiSet<std::less<int>, std::allocator<int>>);
// cannot deduce Key and T from just (Allocator)
static_assert(!CanDeductFlatMultiSet<std::allocator<int>>);
// cannot convert from some arbitrary unrelated type
static_assert(!CanDeductFlatMultiSet<NotAnAllocator>);