Implements Zero-Copy String Views onto Contiguous Memory, resolves #3265.

- http://www.boost.org/doc/libs/1_61_0/libs/utility/doc/html/string_ref.html
- http://en.cppreference.com/w/cpp/string/basic_string_view

include/util/guidance/name_announcements.hpp

@@ -159,13 +159,14 @@ inline bool requiresNameAnnounced(const NameID from_name_id,
     if (from_name_id == to_name_id)
         return false;
     else
-        return requiresNameAnnounced(name_table.GetNameForID(from_name_id),
-                                     name_table.GetRefForID(from_name_id),
-                                     name_table.GetPronunciationForID(from_name_id),
-                                     name_table.GetNameForID(to_name_id),
-                                     name_table.GetRefForID(to_name_id),
-                                     name_table.GetPronunciationForID(to_name_id),
+        return requiresNameAnnounced(name_table.GetNameForID(from_name_id).to_string(),
+                                     name_table.GetRefForID(from_name_id).to_string(),
+                                     name_table.GetPronunciationForID(from_name_id).to_string(),
+                                     name_table.GetNameForID(to_name_id).to_string(),
+                                     name_table.GetRefForID(to_name_id).to_string(),
+                                     name_table.GetPronunciationForID(to_name_id).to_string(),
                                      suffix_table);
+    // FIXME: converts StringViews to strings since the name change heuristics mutates in place
 }
 
 inline bool requiresNameAnnounced(const NameID from_name_id,
@@ -175,12 +176,13 @@ inline bool requiresNameAnnounced(const NameID from_name_id,
     if (from_name_id == to_name_id)
         return false;
     else
-        return requiresNameAnnounced(name_table.GetNameForID(from_name_id),
-                                     name_table.GetRefForID(from_name_id),
-                                     name_table.GetPronunciationForID(from_name_id),
-                                     name_table.GetNameForID(to_name_id),
-                                     name_table.GetRefForID(to_name_id),
-                                     name_table.GetPronunciationForID(to_name_id));
+        return requiresNameAnnounced(name_table.GetNameForID(from_name_id).to_string(),
+                                     name_table.GetRefForID(from_name_id).to_string(),
+                                     name_table.GetPronunciationForID(from_name_id).to_string(),
+                                     name_table.GetNameForID(to_name_id).to_string(),
+                                     name_table.GetRefForID(to_name_id).to_string(),
+                                     name_table.GetPronunciationForID(to_name_id).to_string());
+    // FIXME: converts StringViews to strings since the name change heuristics mutates in place
 }
 
 } // namespace guidance

include/util/name_table.hpp

@@ -3,6 +3,8 @@
 
 #include "util/range_table.hpp"
 #include "util/shared_memory_vector_wrapper.hpp"
+#include "util/string_view.hpp"
+#include "util/typedefs.hpp"
 
 #include <string>
 
@@ -28,9 +30,9 @@ class NameTable
     // The following functions are a subset of what is available.
     // See the data facades for they provide full access to this serialized string data.
     // (at time of writing this: get{Name,Ref,Pronunciation,Destinations}ForID(name_id);)
-    std::string GetNameForID(const unsigned name_id) const;
-    std::string GetRefForID(const unsigned name_id) const;
-    std::string GetPronunciationForID(const unsigned name_id) const;
+    util::StringView GetNameForID(const NameID id) const;
+    util::StringView GetRefForID(const NameID id) const;
+    util::StringView GetPronunciationForID(const NameID id) const;
 };
 } // namespace util
 } // namespace osrm

include/util/string_view.hpp

@@ -0,0 +1,34 @@
+#ifndef OSRM_STRING_VIEW_HPP
+#define OSRM_STRING_VIEW_HPP
+
+#include <boost/functional/hash.hpp>
+#include <boost/utility/string_ref.hpp>
+
+namespace osrm
+{
+namespace util
+{
+// Convenience typedef: boost::string_ref, boost::string_view or C++17's string_view
+using StringView = boost::string_ref;
+
+} // namespace util
+} // namespace osrm
+
+// Specializing hash<> for user-defined type in std namespace, this is standard conforming.
+namespace std
+{
+template <> struct hash<::osrm::util::StringView> final
+{
+    std::size_t operator()(::osrm::util::StringView v) const noexcept
+    {
+        // Bring into scope and call un-qualified for ADL:
+        // remember we want to be able to switch impl. above.
+        using std::begin;
+        using std::end;
+
+        return boost::hash_range(begin(v), end(v));
+    }
+};
+} // namespace std
+
+#endif /* OSRM_STRING_VIEW_HPP */