Use nested namespace

It's a mechanical change to modernize the code base

include/engine/trip/trip_brute_force.hpp

@@ -15,11 +15,7 @@
 #include <string>
 #include <vector>
 
-namespace osrm
-{
-namespace engine
-{
-namespace trip
+namespace osrm::engine::trip
 {
 
 // computes the distance of a given permutation
@@ -93,8 +89,6 @@ inline std::vector<NodeID> BruteForceTrip(const std::size_t number_of_locations,
     return route;
 }
 
-} // namespace trip
-} // namespace engine
 } // namespace osrm
 
 #endif // TRIP_BRUTE_FORCE_HPP

include/engine/trip/trip_farthest_insertion.hpp

@@ -13,11 +13,7 @@
 #include <string>
 #include <vector>
 
-namespace osrm
-{
-namespace engine
-{
-namespace trip
+namespace osrm::engine::trip
 {
 
 // given a route and a new location, find the best place of insertion and
@@ -175,8 +171,6 @@ FarthestInsertionTrip(const std::size_t number_of_locations,
     return FindRoute(number_of_locations, dist_table, max_from, max_to);
 }
 
-} // namespace trip
-} // namespace engine
 } // namespace osrm
 
 #endif // TRIP_FARTHEST_INSERTION_HPP

include/engine/trip/trip_nearest_neighbour.hpp

@@ -13,11 +13,7 @@
 #include <string>
 #include <vector>
 
-namespace osrm
-{
-namespace engine
-{
-namespace trip
+namespace osrm::engine::trip
 {
 
 template <typename NodeIDIterator>
@@ -92,8 +88,6 @@ std::vector<NodeID> NearestNeighbourTrip(const NodeIDIterator &start,
     }
     return route;
 }
-} // namespace trip
-} // namespace engine
 } // namespace osrm
 
 #endif // TRIP_NEAREST_NEIGHBOUR_HPP