Functions: Multi Function

This adds the `MultiFunction` type and some smallish utility types that it uses.
A `MultiFunction` encapsulates a function that is optimized for throughput by
always processing many elements at once.

This is an important part of the new particle system, because it allows us to
execute user generated node trees for many particles efficiently.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D8030

6 files changed, 580 insertions, 3 deletions

diff --git a/tests/gtests/functions/CMakeLists.txt b/tests/gtests/functions/CMakeLists.txt
index 413761ed0c8..f0fe867ea3c 100644
--- a/tests/gtests/functions/CMakeLists.txt
+++ b/tests/gtests/functions/CMakeLists.txt
@@ -36,4 +36,8 @@ if(WITH_BUILDINFO)
   set(BUILDINFO buildinfoobj)
 endif()
 
+BLENDER_TEST(FN_array_spans "bf_blenlib;bf_functions;${BUILDINFO}")
 BLENDER_TEST(FN_cpp_type "bf_blenlib;bf_functions;${BUILDINFO}")
+BLENDER_TEST(FN_generic_vector_array "bf_blenlib;bf_functions;${BUILDINFO}")
+BLENDER_TEST(FN_multi_function "bf_blenlib;bf_functions;${BUILDINFO}")
+BLENDER_TEST(FN_spans "bf_blenlib;bf_functions;${BUILDINFO}")
diff --git a/tests/gtests/functions/FN_array_spans_test.cc b/tests/gtests/functions/FN_array_spans_test.cc
new file mode 100644
index 00000000000..47e1c129266
--- /dev/null
+++ b/tests/gtests/functions/FN_array_spans_test.cc
@@ -0,0 +1,92 @@
+/*
+ * 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.
+ */
+
+#include "testing/testing.h"
+
+#include "FN_array_spans.hh"
+#include "FN_cpp_types.hh"
+
+namespace blender {
+namespace fn {
+
+TEST(virtual_array_span, EmptyConstructor)
+{
+  VArraySpan<int> span;
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(virtual_array_span, SingleArrayConstructor)
+{
+  std::array<int, 4> values = {3, 4, 5, 6};
+  VArraySpan<int> span{Span<int>(values), 3};
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0].size(), 4);
+  EXPECT_EQ(span[1].size(), 4);
+  EXPECT_EQ(span[2].size(), 4);
+  EXPECT_EQ(span[0][0], 3);
+  EXPECT_EQ(span[0][1], 4);
+  EXPECT_EQ(span[0][2], 5);
+  EXPECT_EQ(span[0][3], 6);
+  EXPECT_EQ(span[1][3], 6);
+  EXPECT_EQ(span[2][1], 4);
+}
+
+TEST(virtual_array_span, MultipleArrayConstructor)
+{
+  std::array<int, 4> values0 = {1, 2, 3, 4};
+  std::array<int, 2> values1 = {6, 7};
+  std::array<int, 1> values2 = {8};
+  std::array<const int *, 3> starts = {values0.data(), values1.data(), values2.data()};
+  std::array<uint, 3> sizes{values0.size(), values1.size(), values2.size()};
+
+  VArraySpan<int> span{starts, sizes};
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0].size(), 4);
+  EXPECT_EQ(span[1].size(), 2);
+  EXPECT_EQ(span[2].size(), 1);
+  EXPECT_EQ(&span[0][0], values0.data());
+  EXPECT_EQ(&span[1][0], values1.data());
+  EXPECT_EQ(&span[2][0], values2.data());
+  EXPECT_EQ(span[2][0], 8);
+  EXPECT_EQ(span[1][1], 7);
+}
+
+TEST(generic_virtual_array_span, TypeConstructor)
+{
+  GVArraySpan span{CPPType_int32};
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(generic_virtual_array_span, GSpanConstructor)
+{
+  std::array<std::string, 3> values = {"hello", "world", "test"};
+  GVArraySpan span{GSpan(CPPType_string, values.data(), 3), 5};
+  EXPECT_EQ(span.size(), 5);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0][0], values.data());
+  EXPECT_EQ(span[1][0], values.data());
+  EXPECT_EQ(span[4][0], values.data());
+  EXPECT_EQ(span[0].size(), 3);
+  EXPECT_EQ(span[2].size(), 3);
+  EXPECT_EQ(*(std::string *)span[3][1], "world");
+}
+
+}  // namespace fn
+}  // namespace blender
diff --git a/tests/gtests/functions/FN_cpp_type_test.cc b/tests/gtests/functions/FN_cpp_type_test.cc
index 811e1a5d783..83dc327e381 100644
--- a/tests/gtests/functions/FN_cpp_type_test.cc
+++ b/tests/gtests/functions/FN_cpp_type_test.cc
@@ -12,7 +12,6 @@
  * 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.
- *
  */
 
 #include "testing/testing.h"
@@ -20,7 +19,7 @@
 #include "FN_cpp_type.hh"
 
 namespace blender {
-namespace FN {
+namespace fn {
 
 static const int default_constructed_value = 1;
 static const int copy_constructed_value = 2;
@@ -301,5 +300,5 @@ TEST(cpp_type, FillUninitialized)
   EXPECT_EQ(buffer2[9], 0);
 }
 
-}  // namespace FN
+}  // namespace fn
 }  // namespace blender
diff --git a/tests/gtests/functions/FN_generic_vector_array_test.cc b/tests/gtests/functions/FN_generic_vector_array_test.cc
new file mode 100644
index 00000000000..5840feb955d
--- /dev/null
+++ b/tests/gtests/functions/FN_generic_vector_array_test.cc
@@ -0,0 +1,101 @@
+/*
+ * 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.
+ */
+
+#include "FN_cpp_types.hh"
+#include "FN_generic_vector_array.hh"
+
+#include "testing/testing.h"
+
+namespace blender {
+namespace fn {
+
+TEST(generic_vector_array, Constructor)
+{
+  GVectorArray vectors{CPPType_int32, 3};
+  EXPECT_EQ(vectors.size(), 3);
+  EXPECT_EQ(vectors.lengths().size(), 3);
+  EXPECT_EQ(vectors.starts().size(), 3);
+  EXPECT_EQ(vectors.lengths()[0], 0);
+  EXPECT_EQ(vectors.lengths()[1], 0);
+  EXPECT_EQ(vectors.lengths()[2], 0);
+  EXPECT_EQ(vectors.type(), CPPType_int32);
+}
+
+TEST(generic_vector_array, Append)
+{
+  GVectorArray vectors{CPPType_string, 3};
+  std::string value = "hello";
+  vectors.append(0, &value);
+  value = "world";
+  vectors.append(0, &value);
+  vectors.append(2, &value);
+
+  EXPECT_EQ(vectors.lengths()[0], 2);
+  EXPECT_EQ(vectors.lengths()[1], 0);
+  EXPECT_EQ(vectors.lengths()[2], 1);
+  EXPECT_EQ(vectors[0].size(), 2);
+  EXPECT_EQ(vectors[0].typed<std::string>()[0], "hello");
+  EXPECT_EQ(vectors[0].typed<std::string>()[1], "world");
+  EXPECT_EQ(vectors[2].typed<std::string>()[0], "world");
+}
+
+TEST(generic_vector_array, AsArraySpan)
+{
+  GVectorArray vectors{CPPType_int32, 3};
+  int value = 3;
+  vectors.append(0, &value);
+  vectors.append(0, &value);
+  value = 5;
+  vectors.append(2, &value);
+  vectors.append(2, &value);
+  vectors.append(2, &value);
+
+  GVArraySpan span = vectors;
+  EXPECT_EQ(span.type(), CPPType_int32);
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_EQ(span[0].size(), 2);
+  EXPECT_EQ(span[1].size(), 0);
+  EXPECT_EQ(span[2].size(), 3);
+  EXPECT_EQ(span[0].typed<int>()[1], 3);
+  EXPECT_EQ(span[2].typed<int>()[0], 5);
+}
+
+TEST(generic_vector_array, TypedRef)
+{
+  GVectorArray vectors{CPPType_int32, 4};
+  GVectorArrayRef<int> ref = vectors.typed<int>();
+  ref.append(0, 2);
+  ref.append(0, 6);
+  ref.append(0, 7);
+  ref.append(2, 1);
+  ref.append(2, 1);
+  ref.append(3, 5);
+  ref.append(3, 6);
+
+  EXPECT_EQ(ref[0].size(), 3);
+  EXPECT_EQ(vectors[0].size(), 3);
+  EXPECT_EQ(ref[0][0], 2);
+  EXPECT_EQ(ref[0][1], 6);
+  EXPECT_EQ(ref[0][2], 7);
+  EXPECT_EQ(ref[1].size(), 0);
+  EXPECT_EQ(ref[2][0], 1);
+  EXPECT_EQ(ref[2][1], 1);
+  EXPECT_EQ(ref[3][0], 5);
+  EXPECT_EQ(ref[3][1], 6);
+}
+
+}  // namespace fn
+}  // namespace blender
diff --git a/tests/gtests/functions/FN_multi_function_test.cc b/tests/gtests/functions/FN_multi_function_test.cc
new file mode 100644
index 00000000000..8cd9767abcf
--- /dev/null
+++ b/tests/gtests/functions/FN_multi_function_test.cc
@@ -0,0 +1,222 @@
+/*
+ * 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.
+ */
+
+#include "testing/testing.h"
+
+#include "FN_cpp_types.hh"
+#include "FN_multi_function.hh"
+
+namespace blender {
+namespace fn {
+
+class AddFunction : public MultiFunction {
+ public:
+  AddFunction()
+  {
+    MFSignatureBuilder builder = this->get_builder("Add");
+    builder.single_input<int>("A");
+    builder.single_input<int>("B");
+    builder.single_output<int>("Result");
+  }
+
+  void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
+  {
+    VSpan<int> a = params.readonly_single_input<int>(0, "A");
+    VSpan<int> b = params.readonly_single_input<int>(1, "B");
+    MutableSpan<int> result = params.uninitialized_single_output<int>(2, "Result");
+
+    for (uint i : mask) {
+      result[i] = a[i] + b[i];
+    }
+  }
+};
+
+TEST(multi_function, AddFunction)
+{
+  AddFunction fn;
+
+  Array<int> input1 = {4, 5, 6};
+  Array<int> input2 = {10, 20, 30};
+  Array<int> output(3, -1);
+
+  MFParamsBuilder params(fn, 3);
+  params.add_readonly_single_input(input1.as_span());
+  params.add_readonly_single_input(input2.as_span());
+  params.add_uninitialized_single_output(output.as_mutable_span());
+
+  MFContextBuilder context;
+
+  fn.call({0, 2}, params, context);
+
+  EXPECT_EQ(output[0], 14);
+  EXPECT_EQ(output[1], -1);
+  EXPECT_EQ(output[2], 36);
+}
+
+class AddPrefixFunction : public MultiFunction {
+ public:
+  AddPrefixFunction()
+  {
+    MFSignatureBuilder builder = this->get_builder("Add Prefix");
+    builder.single_input<std::string>("Prefix");
+    builder.single_mutable<std::string>("Strings");
+  }
+
+  void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
+  {
+    VSpan<std::string> prefixes = params.readonly_single_input<std::string>(0, "Prefix");
+    MutableSpan<std::string> strings = params.single_mutable<std::string>(1, "Strings");
+
+    for (uint i : mask) {
+      strings[i] = prefixes[i] + strings[i];
+    }
+  }
+};
+
+TEST(multi_function, AddPrefixFunction)
+{
+  AddPrefixFunction fn;
+
+  Array<std::string> strings = {
+      "Hello",
+      "World",
+      "This is a test",
+      "Another much longer string to trigger an allocation",
+  };
+
+  std::string prefix = "AB";
+
+  MFParamsBuilder params(fn, strings.size());
+  params.add_readonly_single_input(&prefix);
+  params.add_single_mutable(strings.as_mutable_span());
+
+  MFContextBuilder context;
+
+  fn.call({0, 2, 3}, params, context);
+
+  EXPECT_EQ(strings[0], "ABHello");
+  EXPECT_EQ(strings[1], "World");
+  EXPECT_EQ(strings[2], "ABThis is a test");
+  EXPECT_EQ(strings[3], "ABAnother much longer string to trigger an allocation");
+}
+
+class CreateRangeFunction : public MultiFunction {
+ public:
+  CreateRangeFunction()
+  {
+    MFSignatureBuilder builder = this->get_builder("Create Range");
+    builder.single_input<uint>("Size");
+    builder.vector_output<uint>("Range");
+  }
+
+  void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
+  {
+    VSpan<uint> sizes = params.readonly_single_input<uint>(0, "Size");
+    GVectorArrayRef<uint> ranges = params.vector_output<uint>(1, "Range");
+
+    for (uint i : mask) {
+      uint size = sizes[i];
+      for (uint j : IndexRange(size)) {
+        ranges.append(i, j);
+      }
+    }
+  }
+};
+
+TEST(multi_function, CreateRangeFunction)
+{
+  CreateRangeFunction fn;
+
+  GVectorArray ranges(CPPType_uint32, 5);
+  GVectorArrayRef<uint> ranges_ref(ranges);
+  Array<uint> sizes = {3, 0, 6, 1, 4};
+
+  MFParamsBuilder params(fn, ranges.size());
+  params.add_readonly_single_input(sizes.as_span());
+  params.add_vector_output(ranges);
+
+  MFContextBuilder context;
+
+  fn.call({0, 1, 2, 3}, params, context);
+
+  EXPECT_EQ(ranges_ref[0].size(), 3);
+  EXPECT_EQ(ranges_ref[1].size(), 0);
+  EXPECT_EQ(ranges_ref[2].size(), 6);
+  EXPECT_EQ(ranges_ref[3].size(), 1);
+  EXPECT_EQ(ranges_ref[4].size(), 0);
+
+  EXPECT_EQ(ranges_ref[0][0], 0);
+  EXPECT_EQ(ranges_ref[0][1], 1);
+  EXPECT_EQ(ranges_ref[0][2], 2);
+  EXPECT_EQ(ranges_ref[2][0], 0);
+  EXPECT_EQ(ranges_ref[2][1], 1);
+}
+
+class GenericAppendFunction : public MultiFunction {
+ public:
+  GenericAppendFunction(const CPPType &type)
+  {
+    MFSignatureBuilder builder = this->get_builder("Append");
+    builder.vector_mutable("Vector", type);
+    builder.single_input("Value", type);
+  }
+
+  void call(IndexMask mask, MFParams params, MFContext UNUSED(context)) const override
+  {
+    GVectorArray &vectors = params.vector_mutable(0, "Vector");
+    GVSpan values = params.readonly_single_input(1, "Value");
+
+    for (uint i : mask) {
+      vectors.append(i, values[i]);
+    }
+  }
+};
+
+TEST(multi_function, GenericAppendFunction)
+{
+  GenericAppendFunction fn(CPPType_int32);
+
+  GVectorArray vectors(CPPType_int32, 4);
+  GVectorArrayRef<int> vectors_ref(vectors);
+  vectors_ref.append(0, 1);
+  vectors_ref.append(0, 2);
+  vectors_ref.append(2, 6);
+  Array<int> values = {5, 7, 3, 1};
+
+  MFParamsBuilder params(fn, vectors.size());
+  params.add_vector_mutable(vectors);
+  params.add_readonly_single_input(values.as_span());
+
+  MFContextBuilder context;
+
+  fn.call(IndexRange(vectors.size()), params, context);
+
+  EXPECT_EQ(vectors_ref[0].size(), 3);
+  EXPECT_EQ(vectors_ref[1].size(), 1);
+  EXPECT_EQ(vectors_ref[2].size(), 2);
+  EXPECT_EQ(vectors_ref[3].size(), 1);
+
+  EXPECT_EQ(vectors_ref[0][0], 1);
+  EXPECT_EQ(vectors_ref[0][1], 2);
+  EXPECT_EQ(vectors_ref[0][2], 5);
+  EXPECT_EQ(vectors_ref[1][0], 7);
+  EXPECT_EQ(vectors_ref[2][0], 6);
+  EXPECT_EQ(vectors_ref[2][1], 3);
+  EXPECT_EQ(vectors_ref[3][0], 1);
+}
+
+}  // namespace fn
+}  // namespace blender
diff --git a/tests/gtests/functions/FN_spans_test.cc b/tests/gtests/functions/FN_spans_test.cc
new file mode 100644
index 00000000000..551918a3aae
--- /dev/null
+++ b/tests/gtests/functions/FN_spans_test.cc
@@ -0,0 +1,159 @@
+/*
+ * 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.
+ */
+
+#include "testing/testing.h"
+
+#include "FN_cpp_types.hh"
+#include "FN_spans.hh"
+
+namespace blender {
+namespace fn {
+
+TEST(generic_span, TypeConstructor)
+{
+  GSpan span(CPPType_float);
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_EQ(span.typed<float>().size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(generic_span, BufferAndSizeConstructor)
+{
+  int values[4] = {6, 7, 3, 2};
+  void *buffer = (void *)values;
+  GSpan span(CPPType_int32, buffer, 4);
+  EXPECT_EQ(span.size(), 4);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span.typed<int>().size(), 4);
+  EXPECT_EQ(span[0], &values[0]);
+  EXPECT_EQ(span[1], &values[1]);
+  EXPECT_EQ(span[2], &values[2]);
+  EXPECT_EQ(span[3], &values[3]);
+}
+
+TEST(generic_mutable_span, TypeConstructor)
+{
+  GMutableSpan span(CPPType_int32);
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(generic_mutable_span, BufferAndSizeConstructor)
+{
+  int values[4] = {4, 7, 3, 5};
+  void *buffer = (void *)values;
+  GMutableSpan span(CPPType_int32, buffer, 4);
+  EXPECT_EQ(span.size(), 4);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span.typed<int>().size(), 4);
+  EXPECT_EQ(values[2], 3);
+  *(int *)span[2] = 10;
+  EXPECT_EQ(values[2], 10);
+  span.typed<int>()[2] = 20;
+  EXPECT_EQ(values[2], 20);
+}
+
+TEST(virtual_span, EmptyConstructor)
+{
+  VSpan<int> span;
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(virtual_span, SpanConstructor)
+{
+  std::array<int, 5> values = {7, 3, 8, 6, 4};
+  Span<int> span = values;
+  VSpan<int> virtual_span = span;
+  EXPECT_EQ(virtual_span.size(), 5);
+  EXPECT_FALSE(virtual_span.is_empty());
+  EXPECT_EQ(virtual_span[0], 7);
+  EXPECT_EQ(virtual_span[2], 8);
+  EXPECT_EQ(virtual_span[3], 6);
+}
+
+TEST(virtual_span, PointerSpanConstructor)
+{
+  int x0 = 3;
+  int x1 = 6;
+  int x2 = 7;
+  std::array<const int *, 3> pointers = {&x0, &x2, &x1};
+  VSpan<int> span = Span<const int *>(pointers);
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0], 3);
+  EXPECT_EQ(span[1], 7);
+  EXPECT_EQ(span[2], 6);
+  EXPECT_EQ(&span[1], &x2);
+}
+
+TEST(virtual_span, SingleConstructor)
+{
+  int value = 5;
+  VSpan<int> span = VSpan<int>::FromSingle(&value, 3);
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0], 5);
+  EXPECT_EQ(span[1], 5);
+  EXPECT_EQ(span[2], 5);
+  EXPECT_EQ(&span[0], &value);
+  EXPECT_EQ(&span[1], &value);
+  EXPECT_EQ(&span[2], &value);
+}
+
+TEST(generic_virtual_span, TypeConstructor)
+{
+  GVSpan span(CPPType_int32);
+  EXPECT_EQ(span.size(), 0);
+  EXPECT_TRUE(span.is_empty());
+}
+
+TEST(generic_virtual_span, GenericSpanConstructor)
+{
+  int values[4] = {3, 4, 5, 6};
+  GVSpan span{GSpan(CPPType_int32, values, 4)};
+  EXPECT_EQ(span.size(), 4);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0], &values[0]);
+  EXPECT_EQ(span[1], &values[1]);
+  EXPECT_EQ(span[2], &values[2]);
+  EXPECT_EQ(span[3], &values[3]);
+}
+
+TEST(generic_virtual_span, SpanConstructor)
+{
+  std::array<int, 3> values = {6, 7, 8};
+  GVSpan span{Span<int>(values)};
+  EXPECT_EQ(span.type(), CPPType_int32);
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_EQ(span[0], &values[0]);
+  EXPECT_EQ(span[1], &values[1]);
+  EXPECT_EQ(span[2], &values[2]);
+}
+
+TEST(generic_virtual_span, SingleConstructor)
+{
+  int value = 5;
+  GVSpan span = GVSpan::FromSingle(CPPType_int32, &value, 3);
+  EXPECT_EQ(span.size(), 3);
+  EXPECT_FALSE(span.is_empty());
+  EXPECT_EQ(span[0], &value);
+  EXPECT_EQ(span[1], &value);
+  EXPECT_EQ(span[2], &value);
+}
+
+}  // namespace fn
+}  // namespace blender