//===----------------------------------------------------------------------===//
//
// 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

// <span>

// constexpr reference front() const noexcept;
//   Expects: empty() is false.
//   Effects: Equivalent to: return *data();
//


#include <span>
#include <cassert>
#include <string>

#include "test_macros.h"


template <typename Span>
constexpr bool testConstexprSpan(Span sp)
{
    LIBCPP_ASSERT(noexcept(sp.front()));
    return std::addressof(sp.front()) == sp.data();
}


template <typename Span>
void testRuntimeSpan(Span sp)
{
    LIBCPP_ASSERT(noexcept(sp.front()));
    assert(std::addressof(sp.front()) == sp.data());
}

template <typename Span>
void testEmptySpan(Span sp)
{
    if (!sp.empty())
        [[maybe_unused]] auto res = sp.front();
}

struct A{};
constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
          int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};

int main(int, char**)
{
    static_assert(testConstexprSpan(std::span<const int>(iArr1, 1)), "");
    static_assert(testConstexprSpan(std::span<const int>(iArr1, 2)), "");
    static_assert(testConstexprSpan(std::span<const int>(iArr1, 3)), "");
    static_assert(testConstexprSpan(std::span<const int>(iArr1, 4)), "");

    static_assert(testConstexprSpan(std::span<const int, 1>(iArr1, 1)), "");
    static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2)), "");
    static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3)), "");
    static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4)), "");


    testRuntimeSpan(std::span<int>(iArr2, 1));
    testRuntimeSpan(std::span<int>(iArr2, 2));
    testRuntimeSpan(std::span<int>(iArr2, 3));
    testRuntimeSpan(std::span<int>(iArr2, 4));


    testRuntimeSpan(std::span<int, 1>(iArr2, 1));
    testRuntimeSpan(std::span<int, 2>(iArr2, 2));
    testRuntimeSpan(std::span<int, 3>(iArr2, 3));
    testRuntimeSpan(std::span<int, 4>(iArr2, 4));

    std::string s;
    testRuntimeSpan(std::span<std::string>   (&s, 1));
    testRuntimeSpan(std::span<std::string, 1>(&s, 1));

    std::span<int, 0> sp;
    testEmptySpan(sp);

    return 0;
}
