Re: Changing the way dispatch works for built-in functions

[Julien Bect]

Le 13/12/2016 à 00:40, John W. Eaton a écrit :
> While looking at this bug report
>
>   https://savannah.gnu.org/bugs/?49794
>
> I started thinking about how to better handle dispatch for built-in 
> functions.  Currently, built-in functions are found last.  The search 
> is performed in symbol_table::fcn_info::fcn_info_rep::xfind:
>
>
> http://hg.savannah.gnu.org/hgweb/octave/file/9b096bffc10d/libinterp/corefcn/symtab.cc#l647 
>
>
> As things are now, if you create a .m file function with the same name 
> as a built-in function, the .m file function will always override the 
> built-in function.  But, if we were to install built-in functions in 
> the map from class name to function (the same one that is currently 
> only used for user-defined classes) then we could limit the damage 
> someone could do by installing a plain old function with the same name 
> as a built-in.  For example, if we installed the current built-in svd 
> function in the class map for double and single classes, then the 
> built-in svd function would be found when svd is called with a double 
> or single argument.  The only way for a user to accidentally override 
> the built-in version would be to create a function @double/svd 
> @single/svd.

Hi John,

The change that you propose also improves Matlab compatibility.

I have made a quick test on R2016a: creating svd in an ordinary 
directory doesn't override the core svd function for single and double 
argument ; creating the same file a a directory named "@double" does.

@++
Julien