Function deregister_instance_impl

include/pybind11/detail/class.h:355–367

    return true; // unused, but gives the same signature as the deregister func
}
inline bool deregister_instance_impl(void *ptr, instance *self) {
    assert(ptr);
    return with_instance_map(ptr, [&](instance_map &instances) {
        auto range = instances.equal_range(ptr);
        for (auto it = range.first; it != range.second; ++it) {
            if (self == it->second) {
                instances.erase(it);
                return true;
            }
        }
        return false;
    });
}

inline void register_instance(instance *self, void *valptr, const type_info *tinfo) {
    register_instance_impl(valptr, self);