Does optional parameter and optional attribute not supported together?

Question

public void ObjTest(StringBuilder sb, List list, int i = 0,  [Optional] string bs)
{
    ......
 }

The above code throwing compilation er

Answer 1

You can use them in conjunction but the optional parameter (the language construct) must be the last parameter in the parameter list.

public void X(StringBuilder sb, List<string> list, [Optional] string bs, int i = 0)
{
}