Fix for fn call when def argument is interface.

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -2202,9 +2202,11 @@ namespace CppSharp.Generators.CSharp
 
         private string OverloadParamNameWithDefValue(Parameter p, ref int index)
         {
+            Class @class;
             return p.Type.IsPointerToPrimitiveType() && p.Usage == ParameterUsage.InOut && p.HasDefaultValue
                 ? "ref param" + index++
-                : ExpressionPrinter.VisitExpression(p.DefaultArgument).Value;
+                : (( p.Type.TryGetClass(out @class) && @class.IsInterface) ? "param" + index++ 
+                     : ExpressionPrinter.VisitExpression(p.DefaultArgument).Value);
         }
 
         private void GenerateOverloadCall(Function function)
@@ -2221,6 +2223,14 @@ namespace CppSharp.Generators.CSharp
                     WriteLine("{0} param{1} = {2};", pointeeType, j++,
                         primitiveType == PrimitiveType.Bool ? "false" : "0");
                 }
+                Class @class;
+                if (parameter.Kind == ParameterKind.Regular && parameter.Ignore &&
+                    parameter.Type.Desugar().TryGetClass(out @class) && @class.IsInterface &&
+                    parameter.HasDefaultValue)
+                {
+                    WriteLine("var param{0} = ({1}) {2};",  j++, @class.OriginalClass.OriginalName,
+                        ExpressionPrinter.VisitExpression(parameter.DefaultArgument).Value);
+                }
             }
 
             GenerateManagedCall(function);

tests/CSharp/CSharp.cpp

@@ -143,6 +143,10 @@ Bar::Bar(Qux qux)
 {
 }
 
+Bar::Bar(Items item)
+{
+}
+
 int Bar::method()
 {
     return 2;
@@ -471,6 +475,10 @@ void MethodsWithDefaultValues::defaultImplicitCtorEnum(Baz arg)
 {
 }
 
+void MethodsWithDefaultValues::defaultImplicitCtorEnumTwo(Bar arg)
+{
+}
+
 void MethodsWithDefaultValues::defaultIntWithLongExpression(unsigned int i)
 {
 }

tests/CSharp/CSharp.h

@@ -63,6 +63,7 @@ public:
     };
     Bar();
     Bar(Qux qux);
+    Bar(Items item);
     int method();
     const Foo& operator[](int i) const;
     Foo& operator[](int i);
@@ -364,6 +365,7 @@ public:
     // in this case the arg is a MaterializeTemporaryExpr, in the other not
     // I cannot see the difference but it's there so we need both tests
     void defaultImplicitCtorEnum(Baz arg = Bar::Item1);
+    void defaultImplicitCtorEnumTwo(Bar arg = Bar::Items::Item1);
     void defaultIntWithLongExpression(unsigned int i = DEFAULT_INT);
     void defaultRefTypeEnumImplicitCtor(const QColor &fillColor = Qt::white);
     void rotate4x4Matrix(float angle, float x, float y, float z = 0.0f);