Recently it took me a few hours and the help from @hernando to find out the reason of a failure in my code.

Let's say I am trying to make this function

        auto axis = [&] (const std::string& name, const std::string& abbr, AxisDirection dir) {
            return CoordinateSystemAxis::create(
                PropertyMap().set(IdentifiedObject::NAME_KEY, name), abbr,
                dir, UnitOfMeasure::METRE);
        };

Currently it is assigning some garbage to the direction because it is passed by copy, and not by reference. I was calling it with AxisDirection::EAST, that naïvely I supposed it was an enum or enum class.
(the solution is passing the direction by reference... but the compiler was not helping me. The consequence was a crash later in the execution, not a compile error).

The implementation of the create function takes the pointer of the direction (pay attention to the & in &directionIn), that has a "wrong" value if it was copied. The consequence was a later segmentation fault when serializing to JSON.

CoordinateSystemAxisNNPtr CoordinateSystemAxis::create(
    const util::PropertyMap &properties, const std::string &abbreviationIn,
    const AxisDirection &directionIn, const common::UnitOfMeasure &unitIn,
    const MeridianPtr &meridianIn) {
    auto csa(CoordinateSystemAxis::nn_make_shared<CoordinateSystemAxis>());
    csa->setProperties(properties);
    csa->d->abbreviation = abbreviationIn;
    csa->d->direction = &directionIn;
    csa->d->unit = unitIn;
    csa->d->meridian = meridianIn;
    return csa;
}

The easy solution I implement in this PR is deleting the copy and move constructors / assignments operator, so the compiler it not allowing me that wrong operation.

That opens the question: why is it taking a pointer? I find that obscure. But probably changing that implementation may break the API, and would be a lot of work.