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: surf.m
    path of file: ./repos/chebfun/@diskfun
    
    the code of the file until where you have to start completion: function varargout = surf(f, varargin)
%SURF   Surface plot of a DISKFUN.
%   SURF(F) plots the DISKFUN object F on the surface of the unit disk.
%
%   SURF(X, Y, F, ...) calls separableApprox/SURF.  See this function for
%   details.
%
%   SURF(..., 'PropertyName', PropertyValue,...) sets the value of the specified
%   surface property. Multiple property values can be set with a single
%   statement.
%
%   H = SURF(...) returns a handle to the figure.
%
% See also DISKFUN/PLOT and SEPARABLEAPPROX/SURF.

    
function varargout = surf(f, varargin)
%SURF   Surface plot of a DISKFUN.
%   SURF(F) plots the DISKFUN object F on the surface of the unit disk.
%
%   SURF(X, Y, F, ...) calls separableApprox/SURF.  See this function for
%   details.
%
%   SURF(..., 'PropertyName', PropertyValue,...) sets the value of the specified
%   surface property. Multiple property values can be set with a single
%   statement.
%
%   H = SURF(...) returns a handle to the figure.
%
% See also DISKFUN/PLOT and SEPARABLEAPPROX/SURF.

% Empty check:
if ( isempty(f) )
    h = surf([]);
    if ( nargout == 1 )
        varargout = {h};
    end