Add range constructor to generated collections

Author: tmadlener

python/templates/Collection.h.jinja2

@@ -16,6 +16,7 @@
 #include "podio/ICollectionProvider.h"
 #include "podio/CollectionBase.h"
 #include "podio/detail/Pythonizations.h"
+#include "podio/utilities/TypeHelpers.h"
 
 #if defined(PODIO_JSON_OUTPUT) && !defined(__CLING__)
 #include "nlohmann/json_fwd.hpp"
@@ -64,6 +65,11 @@ public:
 
   ~{{ class.bare_type }}Collection() override;
 
+  /// Construct a {{ class.bare_type }} collection from a range of mutable or
+  /// immutable handles
+  template<podio::detail::RangeConvertibleTo<value_type> R>
+  static {{ class.bare_type }}Collection from(R&& range);
+
   constexpr static std::string_view typeName = "{{ (class | string ).strip(':') + "Collection" }}";
   constexpr static std::string_view valueTypeName = "{{ (class | string ).strip(':') }}";
   constexpr static std::string_view dataTypeName = "{{ ( class | string ).strip(':') }}Data";
@@ -236,6 +242,21 @@ Mutable{{ class.bare_type }} {{ class.bare_type }}Collection::create(Args&&... a
   return Mutable{{ class.bare_type }}(podio::utils::MaybeSharedPtr(obj));
 }
 
+template<podio::detail::RangeConvertibleTo<{{ class.bare_type }}Collection::value_type> R>
+{{ class.bare_type }}Collection {{ class.bare_type }}Collection::from(R&& range) {
+  {{ class.bare_type }}Collection coll;
+  if constexpr (podio::detail::RangeOf<R, value_type>) {
+    coll.setSubsetCollection();
+  }
+
+  for (auto elem : range) {
+    coll.push_back(elem);
+  }
+
+  return coll;
+}
+
+
 #if defined(PODIO_JSON_OUTPUT) && !defined(__CLING__)
 void to_json(nlohmann::json& j, const {{ class.bare_type }}Collection& collection);
 #endif

tests/unittests/unittest.cpp

@@ -666,6 +666,33 @@ TEST_CASE("Collection size and empty", "[basics][collections]") {
   REQUIRE(coll.size() == 2u);
 }
 
+TEST_CASE("Collection construction from range", "[basics][collections]") {
+  std::vector<MutableExampleCluster> clusters(10);
+  auto clusterColl = ExampleClusterCollection::from(clusters);
+  REQUIRE_FALSE(clusterColl.isSubsetCollection());
+  REQUIRE(clusterColl.size() == clusters.size());
+  for (size_t i = 0; i < clusters.size(); ++i) {
+    REQUIRE(clusterColl[i] == clusters[i]);
+  }
+
+  const auto otherClusterColl = ExampleClusterCollection::from(std::as_const(clusterColl));
+  REQUIRE(otherClusterColl.isSubsetCollection());
+  REQUIRE(otherClusterColl.size() == clusterColl.size());
+  for (size_t i = 0; i < clusters.size(); ++i) {
+    REQUIRE(otherClusterColl[i] == clusterColl[i]);
+  }
+
+  // Cannot construct a collection from a range of unowned immutable handles
+  REQUIRE_THROWS_AS(ExampleClusterCollection::from(std::vector<ExampleCluster>(10)), std::invalid_argument);
+
+  for (const auto& cluster : clusterColl) {
+    REQUIRE(cluster.id().index != podio::ObjectID::untracked);
+  }
+  // Cannot construct a collection from a range of mutable handles that are
+  // already owned
+  REQUIRE_THROWS_AS(ExampleClusterCollection::from(clusters), std::invalid_argument);
+}
+
 TEST_CASE("const correct indexed access to const collections", "[const-correctness]") {
   STATIC_REQUIRE(std::is_same_v<decltype(std::declval<const ExampleClusterCollection>()[0]),
                                 ExampleCluster>); // const collections should only have indexed access to mutable