switch from json to ordered_json

[gkriger]

Discussed in #3342

^{Originally posted by gkriger February 18, 2022}
From the perspective of casual user the most natural way of switching the code base to ordered_json seems to be replacing

using json = nlohmann::json;

with

using json = nlohmann::ordered_json; 

And the things mostly work. However, this:

json::object_t jobj({ { "product", "one" } });

does not compile however it compiles just fine with using json = nlohmann::json;
Compiler: Microsoft Visual C++ Compiler 16.4.29609.76 (x86_amd64) with c++11 flag.
lib release version 3.10.5

[nlohmann]

I can reproduce the issue with Apple Clang:

In file included from /Users/niels/Code/projects/json-test/cmake-build-debug/_deps/json-src/include/nlohmann/json.hpp:86:
/Users/niels/Code/projects/json-test/cmake-build-debug/_deps/json-src/include/nlohmann/ordered_map.hpp:38:11: error: no matching constructor for initialization of 'std::vector<std::pair<const string, basic_json<nlohmann::ordered_map>>>'
        : Container{init, alloc} {}
          ^        ~~~~~~~~~~~~~
/Users/niels/Code/projects/json-test/main.cpp:8:20: note: in instantiation of member function 'nlohmann::ordered_map<std::string, nlohmann::basic_json<nlohmann::ordered_map>>::ordered_map' requested here
    json::object_t jobj({ { "product", "one" } });
                   ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:560:5: note: candidate constructor not viable: no known conversion from 'std::initializer_list<basic_json<nlohmann::ordered_map>>' to 'const std::vector<std::pair<const std::string, nlohmann::basic_json<nlohmann::ordered_map>>>' for 1st argument
    vector(const vector& __x, const allocator_type& __a);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:569:5: note: candidate constructor not viable: no known conversion from 'initializer_list<nlohmann::basic_json<nlohmann::ordered_map>>' to 'initializer_list<std::vector<std::pair<const std::string, nlohmann::basic_json<nlohmann::ordered_map>>>::value_type>' for 1st argument
    vector(initializer_list<value_type> __il, const allocator_type& __a);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:580:5: note: candidate constructor not viable: no known conversion from 'std::initializer_list<basic_json<nlohmann::ordered_map>>' to 'std::vector<std::pair<const std::string, nlohmann::basic_json<nlohmann::ordered_map>>>' for 1st argument
    vector(vector&& __x, const allocator_type& __a);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:519:5: note: candidate constructor not viable: no known conversion from 'std::initializer_list<basic_json<nlohmann::ordered_map>>' to 'std::vector<std::pair<const std::string, nlohmann::basic_json<nlohmann::ordered_map>>>::size_type' (aka 'unsigned long') for 1st argument
    vector(size_type __n, const value_type& __x);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:522:9: note: candidate template ignored: substitution failure [with _InputIterator = std::initializer_list<nlohmann::basic_json<nlohmann::ordered_map>>]: no type named 'reference' in 'std::iterator_traits<std::initializer_list<nlohmann::basic_json<nlohmann::ordered_map>>>'
        vector(_InputIterator __first,
        ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:537:9: note: candidate template ignored: substitution failure [with _ForwardIterator = std::initializer_list<nlohmann::basic_json<nlohmann::ordered_map>>]: no type named 'reference' in 'std::iterator_traits<std::initializer_list<nlohmann::basic_json<nlohmann::ordered_map>>>'
        vector(_ForwardIterator __first,
        ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:503:40: note: candidate constructor not viable: requires single argument '__a', but 2 arguments were provided
    _LIBCPP_INLINE_VISIBILITY explicit vector(const allocator_type& __a)
                                       ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:515:14: note: candidate constructor not viable: requires single argument '__n', but 2 arguments were provided
    explicit vector(size_type __n);
             ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:559:5: note: candidate constructor not viable: requires single argument '__x', but 2 arguments were provided
    vector(const vector& __x);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:566:5: note: candidate constructor not viable: requires single argument '__il', but 2 arguments were provided
    vector(initializer_list<value_type> __il);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:572:5: note: candidate constructor not viable: requires single argument '__x', but 2 arguments were provided
    vector(vector&& __x)
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:520:5: note: candidate constructor not viable: requires 3 arguments, but 2 were provided
    vector(size_type __n, const value_type& __x, const allocator_type& __a);
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:497:5: note: candidate constructor not viable: requires 0 arguments, but 2 were provided
    vector() _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
    ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:530:9: note: candidate constructor template not viable: requires at least 3 arguments, but 2 were provided
        vector(_InputIterator __first, _InputIterator __last, const allocator_type& __a,
        ^
/Library/Developer/CommandLineTools/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/vector:544:9: note: candidate constructor template not viable: requires at least 3 arguments, but 2 were provided
        vector(_ForwardIterator __first, _ForwardIterator __last, const allocator_type& __a,
        ^
1 error generated.

The issue seems to be a missing constructor in the implementation of ordered_map.

[gkriger]

Great. Are you going to address that in the next release? Is 3.10.5 going to be in Ubuntu 22.04LTS or there is a possibility that this will be fixed there? Feature freeze is close.