def GetGlueCpp(idl_file):
  """Gets the name of the glue implementation file.

  Args:
    idl_file: an idl_parser.File, the source IDL file.

  Returns:
    the name of the implementation file.
  """
  if 'npapi_cpp' in idl_file.__dict__:
    return idl_file.npapi_cpp
  else:
    return idl_file.basename + '_glue.cc'