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: subsref.m
    path of file: ./repos/chebfun/@deltafun
    
    the code of the file until where you have to start completion: function varargout = subsref(f, index)
%SUBSREF   DELTAFUN subsref.
% ( )
%   F(x) tries to evaluate the distribution F at the points given in x.
%   Mathematically, this doesn't make sense when x coincides with a point having
%   a non-trivial delta function. 
% 
%   F(f) [TODO]: tries to compose the distribution F with the linear chebfun f. 
%
% .
%   F.PROP returns the property PROP of F as defined by GET(F, 'PROP').
%
% {}
%   F{S1, S2} restricts F to the subdomain [S1, S2]. See DELTAFUN/RESTRICT for 
%   further details. Note that F{[S1, S2]} is not supported due to the behaviour 
%   of the MATLAB subsref() command.
%   
% See also FEVAL, COMPOSE, GET.

    
function varargout = subsref(f, index)
%SUBSREF   DELTAFUN subsref.
% ( )
%   F(x) tries to evaluate the distribution F at the points given in x.
%   Mathematically, this doesn't make sense when x coincides with a point having
%   a non-trivial delta function. 
% 
%   F(f) [TODO]: tries to compose the distribution F with the linear chebfun f. 
%
% .
%   F.PROP returns the property PROP of F as defined by GET(F, 'PROP').
%
% {}
%   F{S1, S2} restricts F to the subdomain [S1, S2]. See DELTAFUN/RESTRICT for 
%   further details. Note that F{[S1, S2]} is not supported due to the behaviour 
%   of the MATLAB subsref() command.
%   
% See also FEVAL, COMPOSE, GET.

% Copyright 2017 by The University of Oxford and The Chebfun Developers.
% See http://www.chebfun.org/ for Chebfun information.

idx = index(1).subs;
switch index(1).type

%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%% FEVAL / COMPOSE %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    case '()'

        % Where to evaluate:
        x = idx{1}; 
        varin = {};  
                       
        % Deal with additional arguments:
        if ( length(idx) == 2 )
            varin = {idx(2)};
        elseif ( length(idx) > 2 )
            error('CHEBFUN:DELTAFUN:subsref:dimensions', ...
                'Index exceeds chebfun dimensions.')            
        end