Re: st: private vs public mata (user written) functions

[Phil Schumm <pschumm@uchicago.edu>]

On Jul 13, 2006, at 2:14 PM, Zurab Sajaia wrote:
> I have a "public" mata function that is used by a stata command  
> (.ado file). My mata function in turn uses two other "private" mata  
> functions. Either I'm making some other mistake or all three must  
> be added to a library for everything to work and then we have a  
> situation that two "private" functions, which are no use outside of  
> main "public" one are also visible. I know that following Stata's  
> open-source spirit I might end up distributing the un-compiled code  
> anyways but wanted to know for sure if the private/public function  
> setup is possible.

The only way I know of to restrict a function in Mata (i.e., to limit  
where it can be used) is to place its code directly into an ado-file;  
in that case, the function can be used only within that file,  
presumably within the code for the Stata command defined by the  
file.  I believe such functions are referred to as private, with all  
other functions automatically becoming public (i.e., available  
anywhere) by default.

I'm guessing that you've written a Mata function you want to document  
and make available for others to use, and that that function relies  
on a few helper functions which you suspect will not be of interest  
to others, do not wish to document, or perhaps do not even wish to  
share.  In this case, I believe your only option may be to give the  
helper function(s) difficult names so that users are unlikely to call  
them up by accident (e.g., if your function is called my_function_foo 
(), you might call your helpful function _mff_helper()).  Of course,  
if they try, users can still see the names of your helper function(s)  
by using:


    mata describe using <libname>


but if you distribute only the compiled library, they will not be  
able to see the code, and without knowing the API for your helper  
function, they'd be foolish to try to use it.


-- Phil

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