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+/*
+ * 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 __FN_MULTI_FUNCTION_PARAM_TYPE_HH__
+#define __FN_MULTI_FUNCTION_PARAM_TYPE_HH__
+
+/** \file
+ * \ingroup fn
+ *
+ * A multi-function has an arbitrary amount of parameters. Every parameter belongs to one of three
+ * interface types:
+ * - Input: An input parameter is readonly inside the function. The values have to be provided by
+ *     the caller.
+ * - Output: An output parameter has to be initialized by the function. However, the caller
+ *     provides the memory where the data has to be constructed.
+ * - Mutable: A mutable parameter can be considered to be an input and output. The caller has to
+ *     initialize the data, but the function is allowed to modify it.
+ *
+ * Furthermore, every parameter has a MFDataType that describes what kind of data is being passed
+ * around.
+ */
+
+#include "FN_multi_function_data_type.hh"
+
+namespace blender {
+namespace fn {
+
+class MFParamType {
+ public:
+  enum InterfaceType {
+    Input,
+    Output,
+    Mutable,
+  };
+
+  enum Category {
+    SingleInput,
+    VectorInput,
+    SingleOutput,
+    VectorOutput,
+    SingleMutable,
+    VectorMutable,
+  };
+
+ private:
+  InterfaceType m_interface_type;
+  MFDataType m_data_type;
+
+ public:
+  MFParamType(InterfaceType interface_type, MFDataType data_type)
+      : m_interface_type(interface_type), m_data_type(data_type)
+  {
+  }
+
+  static MFParamType ForSingleInput(const CPPType &type)
+  {
+    return MFParamType(InterfaceType::Input, MFDataType::ForSingle(type));
+  }
+
+  static MFParamType ForVectorInput(const CPPType &base_type)
+  {
+    return MFParamType(InterfaceType::Input, MFDataType::ForVector(base_type));
+  }
+
+  static MFParamType ForSingleOutput(const CPPType &type)
+  {
+    return MFParamType(InterfaceType::Output, MFDataType::ForSingle(type));
+  }
+
+  static MFParamType ForVectorOutput(const CPPType &base_type)
+  {
+    return MFParamType(InterfaceType::Output, MFDataType::ForVector(base_type));
+  }
+
+  static MFParamType ForMutableSingle(const CPPType &type)
+  {
+    return MFParamType(InterfaceType::Mutable, MFDataType::ForSingle(type));
+  }
+
+  static MFParamType ForMutableVector(const CPPType &base_type)
+  {
+    return MFParamType(InterfaceType::Mutable, MFDataType::ForVector(base_type));
+  }
+
+  MFDataType data_type() const
+  {
+    return m_data_type;
+  }
+
+  InterfaceType interface_type() const
+  {
+    return m_interface_type;
+  }
+
+  Category category() const
+  {
+    switch (m_data_type.category()) {
+      case MFDataType::Single: {
+        switch (m_interface_type) {
+          case Input:
+            return SingleInput;
+          case Output:
+            return SingleOutput;
+          case Mutable:
+            return SingleMutable;
+        }
+        break;
+      }
+      case MFDataType::Vector: {
+        switch (m_interface_type) {
+          case Input:
+            return VectorInput;
+          case Output:
+            return VectorOutput;
+          case Mutable:
+            return VectorMutable;
+        }
+        break;
+      }
+    }
+    BLI_assert(false);
+    return SingleInput;
+  }
+
+  bool is_input_or_mutable() const
+  {
+    return ELEM(m_interface_type, Input, Mutable);
+  }
+
+  bool is_output_or_mutable() const
+  {
+    return ELEM(m_interface_type, Output, Mutable);
+  }
+
+  friend bool operator==(const MFParamType &a, const MFParamType &b);
+  friend bool operator!=(const MFParamType &a, const MFParamType &b);
+};
+
+inline bool operator==(const MFParamType &a, const MFParamType &b)
+{
+  return a.m_interface_type == b.m_interface_type && a.m_data_type == b.m_data_type;
+}
+
+inline bool operator!=(const MFParamType &a, const MFParamType &b)
+{
+  return !(a == b);
+}
+
+}  // namespace fn
+}  // namespace blender
+
+#endif /* __FN_MULTI_FUNCTION_PARAM_TYPE_HH__ */