Calling sub-function (local function) from another file on Matlab

I'm trying to figure out how to properly call a sub function from another .m file. I've searched for documentation, and only found the way of using function handles (as can be seen here: https://www.mathworks.com/help/matlab/matlab_prog/call-local-functions-using-function-handles.html)

The thing is that I think I've managed to find a way to it without using function handles, and want to know what am i doing and how does it works:

on main.m file:

function main
%function main...
end

function z = sub_function(x,y)
%function sub_function...
end

on outside.m file:
function call_to_local_function_from_outside
z = main('sub_function', x,y);
end

Appernalty, this is working, but why?

[Stephen23]

@Yonatan Nethanel : what MATLAB version are you using?

[Adam]

Your main function takes no input arguments?

[Yonatan Nethanel]

@ Stephen Cobeldick Matlab R2016b

[Yonatan Nethanel]

@Adam my main function is a GUIDE app, and the outside function is also a GUIDE app called from the main GUIDE app

[Stephen23]

@Yonatan Nethanel: please upload the two code files.

[Adam]

One would have to question why you would ever want to call a local function inside a GUI from outside, though. If the function is general enough to make sense to call from outside shouldn't it simply be in its own function file? If it is encapsulated within a GUIDE file (in so much as you could call that encapsulation!) then the whole point should be that it is hidden from the outside I would have thought.

Since there is apparently a Matlab page (in your link) dedicated to digging into files to make calls to local functions I guess there must be some valid use case for it, though I can't think of one.

[Adam Danz]

Here's an approach recommended by the documentation,

https://www.mathworks.com/help/matlab/matlab_prog/call-local-functions-using-function-handles.html

[Oli Fairfax]

Adam, thank you. This worked for me so well. Please put this as an answer so we can vote it.

Answer 1

[Jan]

This would work:

% main.m file: -----------
function out = main(Command, varargin)
switch Command
    case 'sub_function'
        out = sub_function(varargin{:});
    ...
end
end

function z = sub_function(x,y)
z = x + y;
end

% outside.m file: -----------
function outside
x = rand
y = rand
z = main('sub_function', x, y);
end

Although this is working, it is an unnecessary indirection. This increases the level of complexity, because it forwards the local function to global calls. This means drilling a hole into the concept of local or private subfunction. It is leaner and cleaner to move sub_function() to an externally visible function in an own file, when you want to call it from the outside.

A real need to hide a subfunction can be a function name, which is used mutliple times. Then a "package" is usefull: the "+" in the folder name.