You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: topstruct.m
    path of file: ./repos/MatlabGDSPhotonicsToolbox/Functions/GDSII Library/Basic/funcs
    
    the code of the file until where you have to start completion: function [ts] = topstruct(cas, bcell);
%function [ts] = topstruct(cas, bcell);
%
% topstruct :  return the name(s) of the top structure(s)
%              in a cell array of gds_structure objects

    
function [ts] = topstruct(cas, bcell);
%function [ts] = topstruct(cas, bcell);
%
% topstruct :  return the name(s) of the top structure(s)
%              in a cell array of gds_structure objects
%
% cas :   a cell array of gds_structure objects
% bcell : if == 1, a cell array is returned, even when only
%         one top level structure is found.
% ts :    name of the top structure or cell array with names if 
%         the library has more than one top level structure

% Initial version, Ulf Griesmann, December 2012

% check arguments
if nargin < 2, bcell = []; end