Communicating a struct to Fortran with a large array

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What is the best practice for communicating a struct to Fortran that contains a large array object? (In practice, the struct s_t that I define below will also contain other elements).

I was doing something like

using StaticArrays

struct s_t
    fmat::SMatrix{n,m,Cchar,n*m}
end

where n and m are constants.

I then call interface with Fortran using

function test()
    sref = Ref{s_t}()
    ccall((:C_MyRoutine, /path/to/lib.so), Cvoid, (Ref{s_t},), sref)
    return sref[]
end

This is great when n and m are “small”, but as StaticArrays does not work well with large dimensions, this becomes painfully slow in my application.

What is the best way to communicate a struct to Fortran in this case? I can, of course, pass each argument of s_t to a Fortran wrapper individually (where I am now using a regular matrix rather than SMatrix), and reconstruct the derived type in Fortran by copying, but I am wondering what the “best practice” would be in these settings. Thanks.

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