functions in different files

Here is one...

I have a main()-function in main.m, and the file includes a subfunction()-function, like:

function main

b = subfunction(c);

f = external(c);

function b = subfunction(c)

b = c^2;
end

and I have an external()-function in external.m, like

function d = external(e)

d = subfunction(e)*2;

I would like to keep the external()-function in this separate file, but I would like it to be able to use sub-functions in the main file. Now I would have expected, since the main.m is initiated that all subfunctions within it was then "declared" globally, but it turns out that the external function can't call the subfunction, even if it has been called before the external function calls it.

Is there a work-around?

Why? I share the main() with other users, and develop the external() until some point of sharing. Until then I would like to keep it private, but still being able to exploit subfunctions. Alternatively I would need to copy all subfunctions in main() that I need into the external.m or into separate files... But when I share stuff, it is sometimes nice not to send hundreds of files around...

Answer 1

[Mads]

I found a work-around!!

Might be useful to others.

I give the main script an input variable, say 'Fun'. And, say, if Fun=[] then the main() is run as it would be without this trick. Alternatively if main() is called with Fun='test' then main() bypasses its ordinary job and instead runs an "eval('strings = Fun(varargin)')" you know with the correct setting of this string.

So now I can run my external script even from within the main-file and the external script can call functions written inside the main-file.

Voila!

.m:

function Out = main(Fun,In,varargin)
if isempty(Fun)

      %%%%
  else
      if ~isempty(varargin)
          str = 'varargin{1}';
          for n = 2:nargin-2
              str = [str,',varargin{',num2str(n),'}'];
          end
          eval(sprintf('Out = %s(%s);',Fun,str))
      else
          eval(sprintf('Out = %s;',Fun))
      end
  end
end
function a = test(b)
a = b^2;
end

[Stephen23]

Note that this is just the main function calling one of the local functions. Any main function can do this, so this the expected behavior.

Rather than using slow awful eval, you should consider simply using str2func, which would make your code much much faster, neater, easier to debug, easier to read, simpler, etc:

function out = mainFun(str,varargin)
fun = str2func(str);
out = fun(varargin{:});
end
function a = localFun(b) %#ok<DEFNU>
a = b^2;
end

and tested:

>> mainFun('localFun',2)
ans =
     4

Do you see what I did there? By avoiding the slow, buggy, and unnecessary eval, I wrote faster, neater, simpler code.

If you have MATLAB 2013b or more recent you could return the output of the localfunctions

function hnd = mainFun()
hnd = localfunctions;
end
function a = localFun(b) %#ok<DEFNU>
a = b^2;
end

Both of these are going to be much faster and more reliable than any hack code using eval:

https://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

[Mads]

Sure. It was a work around and I didn't know about str2func. It is more elegant. Both ways however solve my problem but I will of course continue with the nicer one.

Answer 2

[Adam]

Sub-functions have file scope. If you want functions to be seen publicly they either need to be each in their own file or they need to be public methods on a class.

Calling the main function of a file has no bearing on external functions suddenly being able to access the local functions of that file - they are effectively like private functions of a class that don't suddenly get exposed when you start using the class.

You can make use of package folders to group functions, but they still need to be in their own file. You can also zip up folders to send them, of course, rather than sending a load of .m files as they are.

Answer 3

[Steven Lord]

Consider making the subfunction a private function instead of a subfunction. This will prevent arbitrary functions from calling it while still making it accessible to the functions in the directory containing the private subdirectory.

[Mads]

Not sure if this would solve my original request of avoiding many directories and files, but can't say I fully understand what you suggest. I'm open to the suggestion though.