+ optional<int> get_layer_id(std::string const &role);
+ optional<struct layer> get_layer(int layer_id) {
+ auto i = std::find_if(std::cbegin(this->mapping),
+ std::cend(this->mapping),
+ [layer_id](struct layer const &l) {
+ return layer_id == l.layer_id;
+ });
+ return i == this->mapping.end() ? nullopt : optional<struct layer>(*i);
+ }
+