Functions: add generic pointer class

This class represents a pointer whose type is only known at runtime.

source/blender/functions/CMakeLists.txt

@@ -38,6 +38,7 @@ set(SRC
   FN_array_spans.hh
   FN_attributes_ref.hh
   FN_cpp_type.hh
+  FN_generic_pointer.hh
   FN_generic_vector_array.hh
   FN_multi_function.hh
   FN_multi_function_builder.hh

source/blender/functions/FN_generic_pointer.hh

@@ -0,0 +1,76 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "FN_cpp_type.hh"
+
+namespace blender::fn {
+
+/**
+ * A generic pointer whose type is only known at runtime.
+ */
+class GMutablePointer {
+ private:
+  const CPPType *type_ = nullptr;
+  void *data_ = nullptr;
+
+ public:
+  GMutablePointer() = default;
+
+  GMutablePointer(const CPPType *type, void *data = nullptr) : type_(type), data_(data)
+  {
+    /* If there is data, there has to be a type. */
+    BLI_assert(data_ == nullptr || type_ != nullptr);
+  }
+
+  GMutablePointer(const CPPType &type, void *data = nullptr) : GMutablePointer(&type, data)
+  {
+  }
+
+  template<typename T> GMutablePointer(T *data) : GMutablePointer(&CPPType::get<T>(), data)
+  {
+  }
+
+  void *get() const
+  {
+    return data_;
+  }
+
+  const CPPType *type() const
+  {
+    return type_;
+  }
+
+  template<typename T> T *get() const
+  {
+    BLI_assert(this->is_type<T>());
+    return reinterpret_cast<T *>(data_);
+  }
+
+  template<typename T> bool is_type() const
+  {
+    return type_ != nullptr && type_->is<T>();
+  }
+
+  void destruct()
+  {
+    BLI_assert(data_ != nullptr);
+    type_->destruct(data_);
+  }
+};
+
+}  // namespace blender::fn