Preserving original order

[KangJH]

Hi
Is there a way to preserve original order of toml file?
This question is similar with #71.
So, I changed my code to use toml::parse<toml::preserve_comments, std::map, std::deque>.
But it still does not preserve original order.
I also tried nlohmann::fifo_map, but it does not seems to support table array and nested table quite well.
Can you recommend a way to preserve original order of toml file?

[ToruNiina]

The serializer dumps the content in the same order as the container has. Since std::map::iterator iterates over the elements from the smallest to the largest, according to the given comparator (by default std::less), the resulting toml file will be sorted by its key. So using std::map does not preserve the order of definition.
I have no idea why nlohmann/fifo_map fails, but you can try another library, for example, https://github.com/Tessil/ordered-map.
For the arrays, std::vector already preserves the order, so you don't need to change it to std::deque.

[KangJH]

Thanks, tsl::ordered_map works perfectly!
FYI, I've changed 2 parts.

1. toml::parse<toml::preserve_comments, tsl::ordered_map, std::vector>(filename)
2. using value = basic_value<preserve_comments, tsl::ordered_map, std::vector>; in value.hpp

When I changed parse part(no.1) only, the nested table was not ordered well.
But, when I applied parsing part and toml::value definition both, it's working well.

Thank you very much
Have a nice day.

[ToruNiina]

Great! And thank you for the detailed information.

The default toml::table is defined as toml::value::table_type. Without modifying the defualt definition of toml::value, after converting a value into toml::table, the elements will be sorted, unexpectedly.

I know it is a confusing behavior. But, AFAIK, there is no way to automatically change the toml::table that is an alias without any template argument depending on the customized toml::value.

Note that, you can obtain the actual table_type used in the toml::basic_value<...> via typename basic_value<...>::table_type.

auto file = toml::parse<toml::preserve_comment, tsl::ordered_map>(filename);
auto tables = toml::find<
        std::vector<typename decltype(file)::table_type>
    >(file, "array_of_table");

But yes, this code looks strange.