Avoiding rewriting accessor methods for new composite types with similar fields

General Usage
4

Other than @forward I can only think of the obvious solutions:

One is

function get_wheel_radius(x :: T) where T
    if hasfield(T, :wheel)  &&  isa(getfield(x, :wheel), Wheel)
        return get_radius(x.wheel)
    else
        error("$T has no wheels")
    end
end

This hard wires field names (not good). One could probably cook up a loop that defines accessor functions for a list of fields without having to repeat the same code over and over again for each field. I doubt that is even less code than @forward.

Another option might be traits. But defining a hasWheel trait for each object also doesn’t look better than @forward.

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