std::complex< T > as attributes

[ax3l]

Hi,

is there a specific reason why we do not allow std::complex< T > types as attributes in ADIOS2?
Those are primitive types and according to my tests in openPMD-api, using complex types as attributes was possible in ADIOS1.

Can we potentially just update the macros that specialize the overloads to allow complex types for attributes as well?

[ax3l]

The specialization you need for nlohmann::json reads:

#include <complex>

namespace std
{
    // std::complex handling
    template< class T > void to_json(nlohmann::json &j, const std::complex< T > &p) {
        j = nlohmann::json {p.real(), p.imag()};
    }

    template< class T > void from_json(const nlohmann::json &j, std::complex< T > &p) {
        p.real(j.at(0));
        p.imag(j.at(1));
    }
}

[ax3l]

Implemented via #1909 and #1922