Fixed error

Author: zillemarco

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -167,7 +167,8 @@ public override bool VisitPointerType(PointerType pointer, TypeQualifiers quals)
                 return true;
             }
 
-            if (finalPointee.IsPrimitiveType(out PrimitiveType primitive) || finalPointee.IsEnumType())
+            PrimitiveType primitive;
+            if (finalPointee.IsPrimitiveType(out primitive) || finalPointee.IsEnumType())
             {
                 if (isRefParam)
                 {
@@ -267,7 +268,8 @@ public override bool VisitTypedefType(TypedefType typedef, TypeQualifiers quals)
 
             var decl = typedef.Declaration;
 
-            if (decl.Type is FunctionType functionType || decl.Type.IsPointerTo(out functionType))
+            var functionType = decl.Type as FunctionType;
+            if (functionType != null || decl.Type.IsPointerTo(out functionType))
             {
                 var ptrName = Generator.GeneratedIdentifier("ptr") +
                     Context.ParameterIndex;
@@ -595,7 +597,9 @@ public override bool VisitPointerType(PointerType pointer, TypeQualifiers quals)
             var param = Context.Parameter;
             var isRefParam = param != null && (param.IsInOut || param.IsOut);
             var finalPointee = pointer.GetFinalPointee();
-            bool finalPointeeIsPrimitiveType = finalPointee.IsPrimitiveType(out PrimitiveType primitive);
+
+            PrimitiveType primitive;
+            bool finalPointeeIsPrimitiveType = finalPointee.IsPrimitiveType(out primitive);
 
             if (CSharpTypePrinter.IsConstCharString(pointee) && isRefParam)
             {