tests/src/unit-iterators2.cpp

//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

// cmake/test.cmake selects the C++ standard versions with which to build a
// unit test based on the presence of JSON_HAS_CPP_<VERSION> macros.
// When using macros that are only defined for particular versions of the standard
// (e.g., JSON_HAS_FILESYSTEM for C++17 and up), please mention the corresponding
// version macro in a comment close by, like this:
// JSON_HAS_CPP_<VERSION> (do not remove; see note at top of file)

#include "doctest_compatibility.h"

#include <nlohmann/json.hpp>
using nlohmann::json;

#include <iterator>

#if JSON_HAS_RANGES
    #include <algorithm>
    #include <ranges>
#endif

TEST_CASE("iterators 2")
{
    SECTION("iterator comparisons")
    {
        json j_values = {nullptr, true, 42, 42u, 23.23, {{"one", 1}, {"two", 2}}, {1, 2, 3, 4, 5}, "Hello, world"};

        for (json& j : j_values)
        {
            auto it1 = j.begin();
            auto it2 = j.begin();
            auto it3 = j.begin();
            ++it2;
            ++it3;
            ++it3;
            auto it1_c = j.cbegin();
            auto it2_c = j.cbegin();
            auto it3_c = j.cbegin();
            ++it2_c;
            ++it3_c;
            ++it3_c;

            // comparison: equal
            {
                CHECK(it1 == it1);
                CHECK(!(it1 == it2));
                CHECK(!(it1 == it3));
                CHECK(!(it2 == it3));
                CHECK(it1_c == it1_c);
                CHECK(!(it1_c == it2_c));
                CHECK(!(it1_c == it3_c));
                CHECK(!(it2_c == it3_c));
            }

            // comparison: not equal
            {
                // check definition
                CHECK( (it1 != it1) == !(it1 == it1) );
                CHECK( (it1 != it2) == !(it1 == it2) );
                CHECK( (it1 != it3) == !(it1 == it3) );
                CHECK( (it2 != it3) == !(it2 == it3) );
                CHECK( (it1_c != it1_c) == !(it1_c == it1_c) );
                CHECK( (it1_c != it2_c) == !(it1_c == it2_c) );
                CHECK( (it1_c != it3_c) == !(it1_c == it3_c) );
                CHECK( (it2_c != it3_c) == !(it2_c == it3_c) );
            }

            // comparison: smaller
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 < it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 < it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c < it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 < it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 < it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c < it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    CHECK(!(it1 < it1));
                    CHECK(it1 < it2);
                    CHECK(it1 < it3);
                    CHECK(it2 < it3);
                    CHECK(!(it1_c < it1_c));
                    CHECK(it1_c < it2_c);
                    CHECK(it1_c < it3_c);
                    CHECK(it2_c < it3_c);
                }
            }

            // comparison: less than or equal
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 <= it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 <= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c <= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 <= it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 <= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c <= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 <= it1) == !(it1 < it1) );
                    CHECK( (it1 <= it2) == !(it2 < it1) );
                    CHECK( (it1 <= it3) == !(it3 < it1) );
                    CHECK( (it2 <= it3) == !(it3 < it2) );
                    CHECK( (it1_c <= it1_c) == !(it1_c < it1_c) );
                    CHECK( (it1_c <= it2_c) == !(it2_c < it1_c) );
                    CHECK( (it1_c <= it3_c) == !(it3_c < it1_c) );
                    CHECK( (it2_c <= it3_c) == !(it3_c < it2_c) );
                }
            }

            // comparison: greater than
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 > it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 > it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c > it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 > it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 > it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c > it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 > it1) == (it1 < it1) );
                    CHECK( (it1 > it2) == (it2 < it1) );
                    CHECK( (it1 > it3) == (it3 < it1) );
                    CHECK( (it2 > it3) == (it3 < it2) );
                    CHECK( (it1_c > it1_c) == (it1_c < it1_c) );
                    CHECK( (it1_c > it2_c) == (it2_c < it1_c) );
                    CHECK( (it1_c > it3_c) == (it3_c < it1_c) );
                    CHECK( (it2_c > it3_c) == (it3_c < it2_c) );
                }
            }

            // comparison: greater than or equal
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 >= it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 >= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c >= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 >= it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 >= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c >= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 >= it1) == !(it1 < it1) );
                    CHECK( (it1 >= it2) == !(it1 < it2) );
                    CHECK( (it1 >= it3) == !(it1 < it3) );
                    CHECK( (it2 >= it3) == !(it2 < it3) );
                    CHECK( (it1_c >= it1_c) == !(it1_c < it1_c) );
                    CHECK( (it1_c >= it2_c) == !(it1_c < it2_c) );
                    CHECK( (it1_c >= it3_c) == !(it1_c < it3_c) );
                    CHECK( (it2_c >= it3_c) == !(it2_c < it3_c) );
                }
            }
        }

        // check exceptions if different objects are compared
        for (auto j : j_values)
        {
            for (auto k : j_values)
            {
                if (j != k)
                {
#if JSON_DIAGNOSTICS
                    // the output differs in each loop, so we cannot fix a string for the expected exception
#else
                    CHECK_THROWS_WITH_AS(j.begin() == k.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.cbegin() == k.cbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.begin() < k.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.cbegin() < k.cbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
#endif
                }
            }
        }
    }

    SECTION("iterator arithmetic")
    {
        json j_object = {{"one", 1}, {"two", 2}, {"three", 3}};
        json j_array = {1, 2, 3, 4, 5, 6};
        json j_null = nullptr;
        json j_value = 42;

        SECTION("addition and subtraction")
        {
            SECTION("object")
            {
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it += 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it += 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it + 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it + 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(1 + it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(1 + it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it -= 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it -= 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it - 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it - 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it - it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it - it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
            }

            SECTION("array")
            {
                {
                    auto it = j_array.begin();
                    it += 3;
                    CHECK((j_array.begin() + 3) == it);
                    CHECK((3 + j_array.begin()) == it);
                    CHECK((it - 3) == j_array.begin());
                    CHECK((it - j_array.begin()) == 3);
                    CHECK(*it == json(4));
                    it -= 2;
                    CHECK(*it == json(2));
                }
                {
                    auto it = j_array.cbegin();
                    it += 3;
                    CHECK((j_array.cbegin() + 3) == it);
                    CHECK((3 + j_array.cbegin()) == it);
                    CHECK((it - 3) == j_array.cbegin());
                    CHECK((it - j_array.cbegin()) == 3);
                    CHECK(*it == json(4));
                    it -= 2;
                    CHECK(*it == json(2));
                }
            }

            SECTION("null")
            {
                {
                    auto it = j_null.begin();
                    it += 3;
                    CHECK((j_null.begin() + 3) == it);
                    CHECK((3 + j_null.begin()) == it);
                    CHECK((it - 3) == j_null.begin());
                    CHECK((it - j_null.begin()) == 3);
                    CHECK(it != j_null.end());
                    it -= 3;
                    CHECK(it == j_null.end());
                }
                {
                    auto it = j_null.cbegin();
                    it += 3;
                    CHECK((j_null.cbegin() + 3) == it);
                    CHECK((3 + j_null.cbegin()) == it);
                    CHECK((it - 3) == j_null.cbegin());
                    CHECK((it - j_null.cbegin()) == 3);
                    CHECK(it != j_null.cend());
                    it -= 3;
                    CHECK(it == j_null.cend());
                }
            }

            SECTION("value")
            {
                {
                    auto it = j_value.begin();
                    it += 3;
                    CHECK((j_value.begin() + 3) == it);
                    CHECK((3 + j_value.begin()) == it);
                    CHECK((it - 3) == j_value.begin());
                    CHECK((it - j_value.begin()) == 3);
                    CHECK(it != j_value.end());
                    it -= 3;
                    CHECK(*it == json(42));
                }
                {
                    auto it = j_value.cbegin();
                    it += 3;
                    CHECK((j_value.cbegin() + 3) == it);
                    CHECK((3 + j_value.cbegin()) == it);
                    CHECK((it - 3) == j_value.cbegin());
                    CHECK((it - j_value.cbegin()) == 3);
                    CHECK(it != j_value.cend());
                    it -= 3;
                    CHECK(*it == json(42));
                }
            }
        }

        SECTION("subscript operator")
        {
            SECTION("object")
            {
                {
                    auto it = j_object.begin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.208] cannot use operator[] for object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.208] cannot use operator[] for object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.cbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.208] cannot use operator[] for object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.208] cannot use operator[] for object iterators", json::invalid_iterator&);
                }
            }

            SECTION("array")
            {
                {
                    auto it = j_array.begin();
                    CHECK(it[0] == json(1));
                    CHECK(it[1] == json(2));
                    CHECK(it[2] == json(3));
                    CHECK(it[3] == json(4));
                    CHECK(it[4] == json(5));
                    CHECK(it[5] == json(6));
                }
                {
                    auto it = j_array.cbegin();
                    CHECK(it[0] == json(1));
                    CHECK(it[1] == json(2));
                    CHECK(it[2] == json(3));
                    CHECK(it[3] == json(4));
                    CHECK(it[4] == json(5));
                    CHECK(it[5] == json(6));
                }
            }

            SECTION("null")
            {
                {
                    auto it = j_null.begin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
                {
                    auto it = j_null.cbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
            }

            SECTION("value")
            {
                {
                    auto it = j_value.begin();
                    CHECK(it[0] == json(42));
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
                {
                    auto it = j_value.cbegin();
                    CHECK(it[0] == json(42));
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
            }
        }
    }

    SECTION("reverse iterator comparisons")
    {
        json j_values = {nullptr, true, 42, 42u, 23.23, {{"one", 1}, {"two", 2}}, {1, 2, 3, 4, 5}, "Hello, world"};

        for (json& j : j_values)
        {
            auto it1 = j.rbegin();
            auto it2 = j.rbegin();
            auto it3 = j.rbegin();
            ++it2;
            ++it3;
            ++it3;
            auto it1_c = j.crbegin();
            auto it2_c = j.crbegin();
            auto it3_c = j.crbegin();
            ++it2_c;
            ++it3_c;
            ++it3_c;

            // comparison: equal
            {
                CHECK(it1 == it1);
                CHECK(!(it1 == it2));
                CHECK(!(it1 == it3));
                CHECK(!(it2 == it3));
                CHECK(it1_c == it1_c);
                CHECK(!(it1_c == it2_c));
                CHECK(!(it1_c == it3_c));
                CHECK(!(it2_c == it3_c));
            }

            // comparison: not equal
            {
                // check definition
                CHECK( (it1 != it1) == !(it1 == it1) );
                CHECK( (it1 != it2) == !(it1 == it2) );
                CHECK( (it1 != it3) == !(it1 == it3) );
                CHECK( (it2 != it3) == !(it2 == it3) );
                CHECK( (it1_c != it1_c) == !(it1_c == it1_c) );
                CHECK( (it1_c != it2_c) == !(it1_c == it2_c) );
                CHECK( (it1_c != it3_c) == !(it1_c == it3_c) );
                CHECK( (it2_c != it3_c) == !(it2_c == it3_c) );
            }

            // comparison: smaller
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 < it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 < it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c < it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 < it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 < it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 < it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c < it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c < it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    CHECK(!(it1 < it1));
                    CHECK(it1 < it2);
                    CHECK(it1 < it3);
                    CHECK(it2 < it3);
                    CHECK(!(it1_c < it1_c));
                    CHECK(it1_c < it2_c);
                    CHECK(it1_c < it3_c);
                    CHECK(it2_c < it3_c);
                }
            }

            // comparison: less than or equal
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 <= it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 <= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c <= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 <= it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 <= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 <= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c <= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c <= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 <= it1) == !(it1 < it1) );
                    CHECK( (it1 <= it2) == !(it2 < it1) );
                    CHECK( (it1 <= it3) == !(it3 < it1) );
                    CHECK( (it2 <= it3) == !(it3 < it2) );
                    CHECK( (it1_c <= it1_c) == !(it1_c < it1_c) );
                    CHECK( (it1_c <= it2_c) == !(it2_c < it1_c) );
                    CHECK( (it1_c <= it3_c) == !(it3_c < it1_c) );
                    CHECK( (it2_c <= it3_c) == !(it3_c < it2_c) );
                }
            }

            // comparison: greater than
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 > it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 > it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c > it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 > it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 > it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 > it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c > it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c > it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 > it1) == (it1 < it1) );
                    CHECK( (it1 > it2) == (it2 < it1) );
                    CHECK( (it1 > it3) == (it3 < it1) );
                    CHECK( (it2 > it3) == (it3 < it2) );
                    CHECK( (it1_c > it1_c) == (it1_c < it1_c) );
                    CHECK( (it1_c > it2_c) == (it2_c < it1_c) );
                    CHECK( (it1_c > it3_c) == (it3_c < it1_c) );
                    CHECK( (it2_c > it3_c) == (it3_c < it2_c) );
                }
            }

            // comparison: greater than or equal
            {
                if (j.type() == json::value_t::object)
                {
#if JSON_DIAGNOSTICS
                    CHECK_THROWS_WITH_AS(it1 >= it1, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it2, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 >= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it3, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it1_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it2_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c >= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it3_c, "[json.exception.invalid_iterator.213] (/5) cannot compare order of object iterators", json::invalid_iterator&);
#else
                    CHECK_THROWS_WITH_AS(it1 >= it1, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it2, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2 >= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1 >= it3, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it1_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it2_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it2_c >= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it1_c >= it3_c, "[json.exception.invalid_iterator.213] cannot compare order of object iterators", json::invalid_iterator&);
#endif
                }
                else
                {
                    // check definition
                    CHECK( (it1 >= it1) == !(it1 < it1) );
                    CHECK( (it1 >= it2) == !(it1 < it2) );
                    CHECK( (it1 >= it3) == !(it1 < it3) );
                    CHECK( (it2 >= it3) == !(it2 < it3) );
                    CHECK( (it1_c >= it1_c) == !(it1_c < it1_c) );
                    CHECK( (it1_c >= it2_c) == !(it1_c < it2_c) );
                    CHECK( (it1_c >= it3_c) == !(it1_c < it3_c) );
                    CHECK( (it2_c >= it3_c) == !(it2_c < it3_c) );
                }
            }
        }

        // check exceptions if different objects are compared
        for (auto j : j_values)
        {
            for (auto k : j_values)
            {
                if (j != k)
                {
#if JSON_DIAGNOSTICS
                    // the output differs in each loop, so we cannot fix a string for the expected exception
#else
                    CHECK_THROWS_WITH_AS(j.rbegin() == k.rbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.crbegin() == k.crbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.rbegin() < k.rbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(j.crbegin() < k.crbegin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator&);
#endif
                }
            }
        }
    }

    SECTION("reverse iterators of a const value")
    {
        const json j_array = {1, 2, 3};
        const json j_object = {{"one", 1}, {"two", 2}};

        // rbegin() and rend() of a const value are crbegin() and crend()
        CHECK(j_array.rbegin() == j_array.crbegin());
        CHECK(j_array.rend() == j_array.crend());
        CHECK(*j_array.rbegin() == 3);
        CHECK(std::distance(j_array.rbegin(), j_array.rend()) == 3);

        CHECK(j_object.rbegin() == j_object.crbegin());
        CHECK(j_object.rend() == j_object.crend());
        CHECK(j_object.rbegin().key() == "two");
        CHECK(std::distance(j_object.rbegin(), j_object.rend()) == 2);
    }

    SECTION("reverse iterator arithmetic")
    {
        json j_object = {{"one", 1}, {"two", 2}, {"three", 3}};
        json j_array = {1, 2, 3, 4, 5, 6};
        json j_null = nullptr;
        json j_value = 42;

        SECTION("addition and subtraction")
        {
            SECTION("object")
            {
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it += 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it += 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it + 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it + 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(1 + it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(1 + it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it -= 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it -= 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it - 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it - 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it - it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it - it, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
            }

            SECTION("array")
            {
                {
                    auto it = j_array.rbegin();
                    it += 3;
                    CHECK((j_array.rbegin() + 3) == it);
                    CHECK(json::reverse_iterator(3 + j_array.rbegin()) == it);
                    CHECK((it - 3) == j_array.rbegin());
                    CHECK((it - j_array.rbegin()) == 3);
                    CHECK(*it == json(3));
                    it -= 2;
                    CHECK(*it == json(5));
                }
                {
                    auto it = j_array.crbegin();
                    it += 3;
                    CHECK((j_array.crbegin() + 3) == it);
                    CHECK(json::const_reverse_iterator(3 + j_array.crbegin()) == it);
                    CHECK((it - 3) == j_array.crbegin());
                    CHECK((it - j_array.crbegin()) == 3);
                    CHECK(*it == json(3));
                    it -= 2;
                    CHECK(*it == json(5));
                }
            }

            SECTION("null")
            {
                {
                    auto it = j_null.rbegin();
                    it += 3;
                    CHECK((j_null.rbegin() + 3) == it);
                    CHECK(json::reverse_iterator(3 + j_null.rbegin()) == it);
                    CHECK((it - 3) == j_null.rbegin());
                    CHECK((it - j_null.rbegin()) == 3);
                    CHECK(it != j_null.rend());
                    it -= 3;
                    CHECK(it == j_null.rend());
                }
                {
                    auto it = j_null.crbegin();
                    it += 3;
                    CHECK((j_null.crbegin() + 3) == it);
                    CHECK(json::const_reverse_iterator(3 + j_null.crbegin()) == it);
                    CHECK((it - 3) == j_null.crbegin());
                    CHECK((it - j_null.crbegin()) == 3);
                    CHECK(it != j_null.crend());
                    it -= 3;
                    CHECK(it == j_null.crend());
                }
            }

            SECTION("value")
            {
                {
                    auto it = j_value.rbegin();
                    it += 3;
                    CHECK((j_value.rbegin() + 3) == it);
                    CHECK(json::reverse_iterator(3 + j_value.rbegin()) == it);
                    CHECK((it - 3) == j_value.rbegin());
                    CHECK((it - j_value.rbegin()) == 3);
                    CHECK(it != j_value.rend());
                    it -= 3;
                    CHECK(*it == json(42));
                }
                {
                    auto it = j_value.crbegin();
                    it += 3;
                    CHECK((j_value.crbegin() + 3) == it);
                    CHECK(json::const_reverse_iterator(3 + j_value.crbegin()) == it);
                    CHECK((it - 3) == j_value.crbegin());
                    CHECK((it - j_value.crbegin()) == 3);
                    CHECK(it != j_value.crend());
                    it -= 3;
                    CHECK(*it == json(42));
                }
            }
        }

        SECTION("subscript operator")
        {
            SECTION("object")
            {
                {
                    auto it = j_object.rbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
                {
                    auto it = j_object.crbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.209] cannot use offsets with object iterators", json::invalid_iterator&);
                }
            }

            SECTION("array")
            {
                {
                    auto it = j_array.rbegin();
                    CHECK(it[0] == json(6));
                    CHECK(it[1] == json(5));
                    CHECK(it[2] == json(4));
                    CHECK(it[3] == json(3));
                    CHECK(it[4] == json(2));
                    CHECK(it[5] == json(1));
                }
                {
                    auto it = j_array.crbegin();
                    CHECK(it[0] == json(6));
                    CHECK(it[1] == json(5));
                    CHECK(it[2] == json(4));
                    CHECK(it[3] == json(3));
                    CHECK(it[4] == json(2));
                    CHECK(it[5] == json(1));
                }
            }

            SECTION("null")
            {
                {
                    auto it = j_null.rbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
                {
                    auto it = j_null.crbegin();
                    CHECK_THROWS_WITH_AS(it[0], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
            }

            SECTION("value")
            {
                {
                    auto it = j_value.rbegin();
                    CHECK(it[0] == json(42));
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
                {
                    auto it = j_value.crbegin();
                    CHECK(it[0] == json(42));
                    CHECK_THROWS_WITH_AS(it[1], "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
                }
            }
        }
    }

#if JSON_HAS_RANGES
    // JSON_HAS_CPP_20 (do not remove; see note at top of file)
    SECTION("ranges")
    {
        SECTION("concepts")
        {
            using nlohmann::detail::iteration_proxy_value;
            CHECK(std::bidirectional_iterator<json::iterator>);
            CHECK(std::input_iterator<iteration_proxy_value<json::iterator>>);

            CHECK(std::is_same<json::iterator, std::ranges::iterator_t<json>>::value);
            CHECK(std::ranges::bidirectional_range<json>);

            using nlohmann::detail::iteration_proxy;
            using items_type = decltype(std::declval<json&>().items());
            CHECK(std::is_same<items_type, iteration_proxy<json::iterator>>::value);
            CHECK(std::is_same<iteration_proxy_value<json::iterator>, std::ranges::iterator_t<items_type>>::value);
            CHECK(std::ranges::input_range<items_type>);
        }

        SECTION("algorithms")
        {
            SECTION("copy")
            {
                json j{"foo", "bar"};
                auto j_copied = json::array();

                std::ranges::copy(j, std::back_inserter(j_copied));

                CHECK(j == j_copied);
            }

            SECTION("find_if")
            {
                json j{1, 3, 2, 4};
                auto j_even = json::array();

#if JSON_USE_IMPLICIT_CONVERSIONS
                auto it = std::ranges::find_if(j, [](int v) noexcept
                {
                    return (v % 2) == 0;
                });
#else
                auto it = std::ranges::find_if(j, [](const json & j) noexcept
                {
                    int v;
                    j.get_to(v);
                    return (v % 2) == 0;
                });
#endif

                CHECK(*it == 2);
            }
        }

        SECTION("views")
        {
            SECTION("reverse")
            {
                json j{1, 2, 3, 4, 5};
                json j_expected{5, 4, 3, 2, 1};

                auto reversed = j | std::views::reverse;
                CHECK(reversed == j_expected);
            }

            SECTION("transform")
            {
                json j
                {
                    { "a_key", "a_value"},
                    { "b_key", "b_value"},
                    { "c_key", "c_value"},
                };
                json j_expected{"a_key", "b_key", "c_key"};

                // NOLINTNEXTLINE(fuchsia-trailing-return)
                auto transformed = j.items() | std::views::transform([](const auto & item) -> std::string_view
                {
                    return item.key();
                });
                auto j_transformed = json::array();
                std::ranges::copy(transformed, std::back_inserter(j_transformed));

                CHECK(j_transformed == j_expected);
            }
        }
    }
#endif
}