Directly parse DBSCAN implementation cmd line option into an enum

examples/dbscan/dbscan.cpp

@@ -296,6 +296,45 @@ void printClusterSizesAndCenters(ExecutionSpace const &exec_space,
     }
   }
 }
+// The type resolution in Boost may require shift operators to be defined in the
+// std namespace.
+namespace std
+{
+// This function is required for Boost program_options to be able to use the
+// Implementation enum.
+std::istream &operator>>(std::istream &in,
+                         ArborX::DBSCAN::Implementation &implementation)
+{
+  std::string impl_string;
+  in >> impl_string;
+
+  if (impl_string == "fdbscan")
+    implementation = ArborX::DBSCAN::Implementation::FDBSCAN;
+  else if (impl_string == "fdbscan-densebox")
+    implementation = ArborX::DBSCAN::Implementation::FDBSCAN_DenseBox;
+  else
+    in.setstate(std::ios_base::failbit);
+
+  return in;
+}
+
+// This function is required for Boost program_options to use Implementation
+// enum as the default_value().
+std::ostream &operator<<(std::ostream &out,
+                         ArborX::DBSCAN::Implementation const &implementation)
+{
+  switch (implementation)
+  {
+  case ArborX::DBSCAN::Implementation::FDBSCAN:
+    out << "fdbscan";
+    break;
+  case ArborX::DBSCAN::Implementation::FDBSCAN_DenseBox:
+    out << "fdbscan-densebox";
+    break;
+  }
+  return out;
+}
+} // namespace std
 
 int main(int argc, char *argv[])
 {
@@ -308,6 +347,7 @@ int main(int argc, char *argv[])
   std::cout << "ArborX hash       : " << ArborX::gitCommitHash() << std::endl;
 
   namespace bpo = boost::program_options;
+  using ArborX::DBSCAN::Implementation;
 
   std::string filename;
   bool binary;
@@ -320,7 +360,7 @@ int main(int argc, char *argv[])
   int max_num_points;
   int num_samples;
   std::string filename_labels;
-  std::string implementation;
+  Implementation implementation;
 
   bpo::options_description desc("Allowed options");
   // clang-format off
@@ -331,7 +371,7 @@ int main(int argc, char *argv[])
       ( "core-min-size", bpo::value<int>(&core_min_size)->default_value(2), "DBSCAN min_pts")
       ( "eps", bpo::value<float>(&eps), "DBSCAN eps" )
       ( "filename", bpo::value<std::string>(&filename), "filename containing data" )
-      ( "impl", bpo::value<std::string>(&implementation)->default_value("fdbscan"), "implementation (\"fdbscan\" or \"fdbscan-densebox\")")
+      ( "impl", bpo::value<Implementation>(&implementation)->default_value(Implementation::FDBSCAN), "implementation (\"fdbscan\" or \"fdbscan-densebox\")")
       ( "labels", bpo::value<std::string>(&filename_labels)->default_value(""), "clutering results output" )
       ( "max-num-points", bpo::value<int>(&max_num_points)->default_value(-1), "max number of points to read in")
       ( "output-sizes-and-centers", bpo::bool_switch(&print_sizes_centers)->default_value(false), "print cluster sizes and centers")
@@ -350,16 +390,8 @@ int main(int argc, char *argv[])
     return 1;
   }
 
-  if (implementation != "fdbscan" && implementation != "fdbscan-densebox")
-  {
-    std::cout << "Unknown implementation: \"" << implementation
-              << "\". Valid values are [\"fdbscan\", \"fdbscan-densebox\"]."
-              << std::endl;
-    return 2;
-  }
-  auto impl = (implementation == "fdbscan"
-                   ? ArborX::DBSCAN::Implementation::FDBSCAN
-                   : ArborX::DBSCAN::Implementation::FDBSCAN_DenseBox);
+  std::stringstream ss;
+  ss << implementation;
 
   // Print out the runtime parameters
   printf("eps               : %f\n", eps);
@@ -368,7 +400,7 @@ int main(int argc, char *argv[])
   printf("filename          : %s [%s, max_pts = %d]\n", filename.c_str(),
          (binary ? "binary" : "text"), max_num_points);
   printf("filename [labels] : %s [binary]\n", filename_labels.c_str());
-  printf("implementation    : %s\n", implementation.c_str());
+  printf("implementation    : %s\n", ss.str().c_str());
   printf("samples           : %d\n", num_samples);
   printf("verify            : %s\n", (verify ? "true" : "false"));
   printf("print timers      : %s\n", (print_dbscan_timers ? "true" : "false"));
@@ -403,7 +435,7 @@ int main(int argc, char *argv[])
   auto labels = ArborX::dbscan(exec_space, primitives, eps, core_min_size,
                                ArborX::DBSCAN::Parameters()
                                    .setPrintTimers(print_dbscan_timers)
-                                   .setImplementation(impl));
+                                   .setImplementation(implementation));
 
   timer_start(timer);
   Kokkos::View<int *, MemorySpace> cluster_indices("Testing::cluster_indices",