How to get reference of std::vector<T>

[pschmale-grimme]

Hi,
thanks for this awesome library. I've got a json file with an array of strings and I am wondering if it would be possible to get a reference of std::vectorstd::string?

{ "array": ["val1", "val2"]}

This code is working fine:

nlohmann::json fileContent = json::parse(...);
std::vector<std::string> array = fileContent["array"].get<std::vector<std::string>>();

But trying to get a reference doesn't:

const std::vector<std::string>& array = fileContent["array"].get_ref<const std::vector<std::string>&>();

GCC complains about error: no matching function for call to ‘nlohmann::basic_json<>::get_impl_ptr(const std::vector<std::__cxx11::basic_string<char> >*) const’

Would it be possible to fix this?

[nickaein]

Based on get_ref() documentation, it supports only the basic json types (e.g. array_t). I doubt a zero-cost cast is be possible from the underlying json type to std::vector<std::string>. This is in contrast to get() method which can create a fresh copy of given type if needed.

You can still get a reference to the array though. Here is an demo: https://godbolt.org/z/9o5Yrv4zE
Note that I have modified the array just for demonstration and I'm not sure if this is allowed.

[nlohmann]

You cannot convert references - the values are internally stored as array_t<json> (with std::vector being the default type for array_t), so @nickaein is right that get_ref<json::array_t&>() is as far as you can go.

[pschmale-grimme]

Thanks for your help. I think using a reference to array_t isn't an option for me. Im my application I have one module 'A' which parses some json config and some other module 'B' which uses the parsed values. I would like module 'B' to stay independent from the json library.
The array in the config won't be big and so I can will live with the copy of std::vector<std::string> instead.