Replace boost::optional with std::optional (#6611)

include/guidance/intersection_handler.hpp

@@ -15,11 +15,10 @@
 
 #include <algorithm>
 #include <cstddef>
+#include <optional>
 #include <utility>
 #include <vector>
 
-#include <boost/optional.hpp>
-
 namespace osrm::guidance
 {
 
@@ -129,7 +128,7 @@ class IntersectionHandler
     //     ^ via
     //
     // For this scenario returns intersection at `b` and `b`.
-    boost::optional<IntersectionHandler::IntersectionViewAndNode>
+    std::optional<IntersectionHandler::IntersectionViewAndNode>
     getNextIntersection(const NodeID at, const EdgeID via) const;
 
     bool isSameName(const EdgeID source_edge_id, const EdgeID target_edge_id) const;

include/guidance/sliproad_handler.hpp

@@ -9,10 +9,9 @@
 
 #include "util/node_based_graph.hpp"
 
+#include <optional>
 #include <vector>
 
-#include <boost/optional.hpp>
-
 namespace osrm::guidance
 {
 
@@ -43,9 +42,9 @@ class SliproadHandler final : public IntersectionHandler
                             Intersection intersection) const override final;
 
   private:
-    boost::optional<std::size_t> getObviousIndexWithSliproads(const EdgeID from,
-                                                              const Intersection &intersection,
-                                                              const NodeID at) const;
+    std::optional<std::size_t> getObviousIndexWithSliproads(const EdgeID from,
+                                                            const Intersection &intersection,
+                                                            const NodeID at) const;
 
     // Next intersection from `start` onto `onto` is too far away for a Siproad scenario
     bool nextIntersectionIsTooFarAway(const NodeID start, const EdgeID onto) const;

include/guidance/turn_handler.hpp

@@ -11,9 +11,8 @@
 #include "util/attributes.hpp"
 #include "util/node_based_graph.hpp"
 
-#include <boost/optional.hpp>
-
 #include <cstddef>
+#include <optional>
 #include <utility>
 #include <vector>
 
@@ -72,7 +71,7 @@ class TurnHandler final : public IntersectionHandler
 
     bool hasObvious(const EdgeID &via_edge, const Fork &fork) const;
 
-    boost::optional<Fork> findForkCandidatesByGeometry(Intersection &intersection) const;
+    std::optional<Fork> findForkCandidatesByGeometry(Intersection &intersection) const;
 
     bool isCompatibleByRoadClass(const Intersection &intersection, const Fork fork) const;
 
@@ -96,7 +95,7 @@ class TurnHandler final : public IntersectionHandler
     handleDistinctConflict(const EdgeID via_edge, ConnectedRoad &left, ConnectedRoad &right) const;
 
     // Classification
-    boost::optional<Fork> findFork(const EdgeID via_edge, Intersection &intersection) const;
+    std::optional<Fork> findFork(const EdgeID via_edge, Intersection &intersection) const;
 
     OSRM_ATTR_WARN_UNUSED
     Intersection assignLeftTurns(const EdgeID via_edge,