Warning when passing arguments to a GUIDE GUI - matlab

Question

I am trying to pass arguments to a GUIDE generated GUI. This works but throws a Warning.
inputTest('Passed In String')
Warning: The input to STR2FUNC "Passed In String" is not a valid
function name. This will generate an error in a future release.
I know I have passed arguments to GUIDE GUIs in the past and I don't recall ever seeing this warning message before. However, I am relatively new to Matlab 2016b so something may have changed that I am not aware of. I didn't find anything in the documentation.
The warning occurs in the "initialization code - DO NOT EDIT" auto generated section and only happens when passing in an optional argument.
Is this a bug in 2016b or have I missed something?
Minimal Example below. It is a simple GUI with only a single Edit box.
function varargout = inputTest(varargin)
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', #inputTest_OpeningFcn, ...
'gui_OutputFcn', #inputTest_OutputFcn, ...
'gui_LayoutFcn', [] , ...
'gui_Callback', []);
if nargin && ischar(varargin{1})
gui_State.gui_Callback = str2func(varargin{1}); % WARNING OCCURS HERE
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
function inputTest_OpeningFcn(hObject, eventdata, handles, varargin)
handles.output = hObject;
% Fill the box if the string is passed in.
if nargin == 4
handles.edit1.String = varargin{1};
else
handles.edit1.String = 'Nothing Passed In';
end
guidata(hObject, handles);
function varargout = inputTest_OutputFcn(hObject, eventdata, handles)
varargout{1} = handles.output;
function edit1_Callback(hObject, eventdata, handles)
function edit1_CreateFcn(hObject, eventdata, handles)
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end

Answer 1

The default GUIDE GUI behavior is explained in the autogenerated inline documentation:
% ASDF MATLAB code for asdf.fig
% ASDF, by itself, creates a new ASDF or raises the existing
% singleton*.
%
% H = ASDF returns the handle to a new ASDF or the handle to
% the existing singleton*.
%
% ASDF('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in ASDF.M with the given input arguments.
%
% ASDF('Property','Value',...) creates a new ASDF or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before asdf_OpeningFcn gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to asdf_OpeningFcn via varargin.
The syntax you're attempting to use is the syntax reserved for calling callbacks that are local to your GUI, which is why it's using a str2func call on the first input. Either remove the str2func call or change your input syntax to accept a separate output than what GUIDE is designed for.