ENH: New functions getEnumNameFromValue() and getEnumValueFromName()

Summary

See title.

Focus

Do the new functions cover the use cases of higher-order client libraries?

Test Environment

make test, look into test_utility.cpp.

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• I understand the intent of this MR
• All automated tests pass
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src/caosdb/utility.cpp

+/*
+ * This file is a part of the CaosDB Project.
+ *
+ * Copyright (C) 2021 Daniel Hornung <d.hornung@indiscale.com>
+ * Copyright (C) 2021 IndiScale GmbH <info@indiscale.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+ */
+#include "caosdb/data_type.h"
+#include "caosdb/entity.h"
+#include "caosdb/utility.h"
+#include <algorithm>
+
+namespace caosdb::utility {
+
+using caosdb::entity::AtomicDataType;
+using caosdb::entity::Importance;
+using caosdb::entity::Role;
+
+// using emap = std::map<int, std::string>;          // enum mapping
+
+// Enum helper template specializations //////////////////////////////////////
+template <> auto getEnumNameFromValue<Importance>(Importance v) -> std::string {
+  auto result = caosdb::entity::importance_names.at(v);
+  return result;
+}
+
+template <> auto getEnumNameFromValue<Role>(Role v) -> std::string {
+  auto result = caosdb::entity::role_names.at(v);
+  return result;
+}
+
+template <> auto getEnumNameFromValue<AtomicDataType>(AtomicDataType v) -> std::string {
+  auto result = caosdb::entity::atomicdatatype_names.at(v);
+  return result;
+}
+
+template <> auto getEnumValueFromName<Importance>(const std::string &name) -> Importance {
+  // TODO (dh): Why does this compile?
+  // if (caosdb::entity::importance_names.begin()->second == name) {}
+  // std::for_each(caosdb::entity::importance_names.begin(),
+  //               caosdb::entity::importance_names.end(),
+  //               [](const auto &entry){});
+  // TODO (dh): Whereas this does not?
+  // auto result = std::find(caosdb::entity::importance_names.cbegin(),
+  //                         caosdb::entity::importance_names.cend(),
+  //                         [name](const auto& entry){ return entry.second == name; });
+  // Workaround: plaint old iteration:
+  for (auto const &entry : caosdb::entity::importance_names) {
+    if (entry.second == name) {
+      return entry.first;
+    }
+  }
+  throw std::out_of_range(std::string("Could not find enum value for string '") + name + "'.");
+}
+
+template <> auto getEnumValueFromName<AtomicDataType>(const std::string &name) -> AtomicDataType {
+  for (auto const &entry : caosdb::entity::atomicdatatype_names) {
+    if (entry.second == name) {
+      return entry.first;
+    }
+  }
+  throw std::out_of_range(std::string("Could not find enum value for string '") + name + "'.");
+}
+
+template <> auto getEnumValueFromName<Role>(const std::string &name) -> Role {
+  for (auto const &entry : caosdb::entity::role_names) {
+    if (entry.second == name) {
+      return entry.first;
+    }
+  }
+  throw std::out_of_range(std::string("Could not find enum value for string '") + name + "'.");
+}
+
+// End of template specialization /////////////////////////////////////////////
+
+} // namespace caosdb::utility