Check does field have default defined?

[ahojukka5]

Can I verify whether a specific field has a default value? I'm looking to dynamically construct a struct and configure it using a named tuple, but I want to do this only for fields that don't have predefined defaults.

@with_kw struct Model
    Lx::Int=128
    Ly::Int=128
    M::Matrix
end

function has_default(Model, fieldname)
    # ....?
end

function create(Model, settings)
    defaults = Dict()
    for (fieldname, fieldtype) in zip(fieldnames(Model), fieldtypes(Model))
        if fieldtype == Matrix && !has_default(Model, fieldname)
            defaults[fieldname] = fieldtype(undef, settings.Lx, settings.Ly)
        end
    end
    return Model(; settings..., defaults...)
end