all of the changes

tests/b205_regression.cpp

@@ -5,6 +5,7 @@
 #include <iostream>
 #include <stdexcept>
 #include <vector>
+#include <span>
 
 using namespace fluidsim::port;
 namespace {
@@ -14,7 +15,8 @@ void check(bool condition, const char* message) {
 }
 int main() {
     SaabB205Scenario s;
-    const auto cylinders = s.cylinders();
+    const auto storage = s.cylinders();
+    const std::span<FourStrokeCylinder* const> cylinders(storage.data(), s.cylinder_count());
     check(s.cylinder_count() == 4 && s.pipes.size() == 10, "B205 topology is not four-cylinder");
     check(std::abs(4*s.cylinder1.swept_volume()*1e6f-1984.9f) < 1, "B205 displacement incorrect");
     check(s.vehicle.gear_ratios.size() == 5 && s.vehicle.mass == 1675, "wagon configuration incorrect");