Method generalize

src/ifcparse/aggregate_of_instance.h:85–91

    it end() { return list_.end(); }
    size_t size() const { return list_.size(); }
    aggregate_of_instance::ptr generalize() {
        aggregate_of_instance::ptr result(new aggregate_of_instance());
        for (it i = begin(); i != end(); ++i) {
            result->push((*i)->template as<IfcUtil::IfcBaseClass>());
        }
        return result;
    }
    bool contains(T* type) const { return std::find(list_.begin(), list_.end(), type) != list_.end(); }
    template <class U>
    typename U::list::ptr as() {