Workaround for the syntax error in C#:ref and out are not valid in this context

Recently I was  trying  to implement the interface Microsoft.Office.Interop.Word.Styles.
public Style this[ref object Index]
        {
          
        }

Visual Studio through  this error ":ref and out are not valid in this context"

Workaround :

//public Style this[ref object Index] // error CS0631: ref and out are not valid in this context
public Style get_Item(ref object Index)
{
    . . .
}