3 files changed, 243 insertions, 0 deletions
diff --git a/source/blender/blenlib/BLI_multi_value_map.hh b/source/blender/blenlib/BLI_multi_value_map.hh
new file mode 100644
index 00000000000..ca7a369ed29
--- /dev/null
+++ b/source/blender/blenlib/BLI_multi_value_map.hh
@@ -0,0 +1,133 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __BLI_MULTI_VALUE_MAP_HH__
+#define __BLI_MULTI_VALUE_MAP_HH__
+
+/** \file
+ * \ingroup bli
+ *
+ * A `blender::MultiValueMap<Key, Value>` is an unordered associative container that stores
+ * key-value pairs. It is different from `blender::Map` in that it can store multiple values for
+ * the same key. The list of values that corresponds to a specific key can contain duplicates.
+ *
+ * This data structure is different from a `std::multi_map`, because multi_map can store the same
+ * key more than once and MultiValueMap can't.
+ *
+ * Currently, this class exists mainly for convenience. There are no performance benefits over
+ * using Map<Key, Vector<Value>>. In the future, a better implementation for this data structure
+ * can be developed.
+ */
+
+#include "BLI_map.hh"
+#include "BLI_vector.hh"
+
+namespace blender {
+
+template<typename Key, typename Value> class MultiValueMap {
+ private:
+  using MapType = Map<Key, Vector<Value>>;
+  MapType map_;
+
+ public:
+  /**
+   * Add a new value for the given key. If the map contains the key already, the value will be
+   * appended to the list of corresponding values.
+   */
+  void add(const Key &key, const Value &value)
+  {
+    this->add_as(key, value);
+  }
+  void add(const Key &key, Value &&value)
+  {
+    this->add_as(key, std::move(value));
+  }
+  void add(Key &&key, const Value &value)
+  {
+    this->add_as(std::move(key), value);
+  }
+  void add(Key &&key, Value &&value)
+  {
+    this->add_as(std::move(key), std::move(value));
+  }
+  template<typename ForwardKey, typename ForwardValue>
+  void add_as(ForwardKey &&key, ForwardValue &&value)
+  {
+    Vector<Value> &vector = map_.lookup_or_add_default_as(std::forward<ForwardKey>(key));
+    vector.append(std::forward<ForwardValue>(value));
+  }
+
+  /**
+   * Add all given values to the key.
+   */
+  void add_multiple(const Key &key, Span<Value> values)
+  {
+    this->add_multiple_as(key, values);
+  }
+  void add_multiple(Key &&key, Span<Value> values)
+  {
+    this->add_multiple_as(std::move(key), values);
+  }
+  template<typename ForwardKey> void add_multiple_as(ForwardKey &&key, Span<Value> values)
+  {
+    Vector<Value> &vector = map_.lookup_or_add_default_as(std::forward<ForwardKey>(key));
+    vector.extend(values);
+  }
+
+  /**
+   * Get a span to all the values that are stored for the given key.
+   */
+  Span<Value> lookup(const Key &key) const
+  {
+    return this->lookup_as(key);
+  }
+  template<typename ForwardKey> Span<Value> lookup_as(const ForwardKey &key) const
+  {
+    const Vector<Value> *vector = map_.lookup_ptr_as(key);
+    if (vector != nullptr) {
+      return vector->as_span();
+    }
+    return {};
+  }
+
+  /**
+   * Note: This signature will change when the implementation changes.
+   */
+  typename MapType::ItemIterator items() const
+  {
+    return map_.items();
+  }
+
+  /**
+   * Note: This signature will change when the implementation changes.
+   */
+  typename MapType::KeyIterator keys() const
+  {
+    return map_.keys();
+  }
+
+  /**
+   * Note: This signature will change when the implementation changes.
+   */
+  typename MapType::ValueIterator values() const
+  {
+    return map_.values();
+  }
+};
+
+}  // namespace blender
+
+#endif /* __BLI_MULTI_VALUE_MAP_HH__ */
diff --git a/source/blender/blenlib/CMakeLists.txt b/source/blender/blenlib/CMakeLists.txt
index db44ebe8e55..4997917a93f 100644
--- a/source/blender/blenlib/CMakeLists.txt
+++ b/source/blender/blenlib/CMakeLists.txt
@@ -353,6 +353,7 @@ if(WITH_GTESTS)
     tests/BLI_map_test.cc
     tests/BLI_math_base_safe_test.cc
     tests/BLI_memory_utils_test.cc
+    tests/BLI_multi_value_map_test.cc
     tests/BLI_set_test.cc
     tests/BLI_span_test.cc
     tests/BLI_stack_cxx_test.cc
diff --git a/source/blender/blenlib/tests/BLI_multi_value_map_test.cc b/source/blender/blenlib/tests/BLI_multi_value_map_test.cc
new file mode 100644
index 00000000000..7501fbe0d87
--- /dev/null
+++ b/source/blender/blenlib/tests/BLI_multi_value_map_test.cc
@@ -0,0 +1,109 @@
+/* Apache License, Version 2.0 */
+
+#include "BLI_multi_value_map.hh"
+#include "BLI_vector.hh"
+#include "testing/testing.h"
+
+namespace blender::tests {
+
+TEST(multi_value_map, LookupNotExistant)
+{
+  MultiValueMap<int, int> map;
+  EXPECT_EQ(map.lookup(5).size(), 0);
+  map.add(2, 5);
+  EXPECT_EQ(map.lookup(5).size(), 0);
+}
+
+TEST(multi_value_map, LookupExistant)
+{
+  MultiValueMap<int, int> map;
+  map.add(2, 4);
+  map.add(2, 5);
+  map.add(3, 6);
+
+  EXPECT_EQ(map.lookup(2).size(), 2);
+  EXPECT_EQ(map.lookup(2)[0], 4);
+  EXPECT_EQ(map.lookup(2)[1], 5);
+
+  EXPECT_EQ(map.lookup(3).size(), 1);
+  EXPECT_EQ(map.lookup(3)[0], 6);
+}
+
+TEST(multi_value_map, AddMultiple)
+{
+  MultiValueMap<int, int> map;
+  map.add_multiple(2, {4, 5, 6});
+  map.add_multiple(2, {1, 2});
+  map.add_multiple(5, {7, 5, 3});
+
+  EXPECT_EQ(map.lookup(2).size(), 5);
+  EXPECT_EQ(map.lookup(2)[0], 4);
+  EXPECT_EQ(map.lookup(2)[1], 5);
+  EXPECT_EQ(map.lookup(2)[2], 6);
+  EXPECT_EQ(map.lookup(2)[3], 1);
+  EXPECT_EQ(map.lookup(2)[4], 2);
+
+  EXPECT_EQ(map.lookup(5).size(), 3);
+  EXPECT_EQ(map.lookup(5)[0], 7);
+  EXPECT_EQ(map.lookup(5)[1], 5);
+  EXPECT_EQ(map.lookup(5)[2], 3);
+}
+
+TEST(multi_value_map, Keys)
+{
+  MultiValueMap<int, int> map;
+  map.add(5, 7);
+  map.add(5, 7);
+  map.add_multiple(2, {6, 7, 8});
+
+  Vector<int> keys;
+  for (int key : map.keys()) {
+    keys.append(key);
+  }
+
+  EXPECT_EQ(keys.size(), 2);
+  EXPECT_TRUE(keys.contains(5));
+  EXPECT_TRUE(keys.contains(2));
+}
+
+TEST(multi_value_map, Values)
+{
+  MultiValueMap<int, int> map;
+  map.add(3, 5);
+  map.add_multiple(3, {1, 2});
+  map.add(6, 1);
+
+  Vector<Span<int>> values;
+  for (Span<int> value_span : map.values()) {
+    values.append(value_span);
+  }
+
+  EXPECT_EQ(values.size(), 2);
+}
+
+TEST(multi_value_map, Items)
+{
+  MultiValueMap<int, int> map;
+  map.add_multiple(4, {1, 2, 3});
+
+  for (auto &&item : map.items()) {
+    int key = item.key;
+    Span<int> values = item.value;
+    EXPECT_EQ(key, 4);
+    EXPECT_EQ(values.size(), 3);
+    EXPECT_EQ(values[0], 1);
+    EXPECT_EQ(values[1], 2);
+    EXPECT_EQ(values[2], 3);
+  }
+}
+
+TEST(multi_value_map, UniquePtr)
+{
+  /* Mostly testing if it compiles here. */
+  MultiValueMap<std::unique_ptr<int>, std::unique_ptr<int>> map;
+  map.add(std::make_unique<int>(4), std::make_unique<int>(6));
+  map.add(std::make_unique<int>(4), std::make_unique<int>(7));
+  EXPECT_EQ(map.lookup(std::make_unique<int>(10)).size(), 0);
+}
+
+}  // namespace blender::tests