Re: Using exceptions in the core

[Jordi Gutiérrez Hermoso]

On Sun, 2015-09-27 at 10:38 +0200, Olaf Till wrote:
> On Sat, Sep 26, 2015 at 12:13:03PM -0400, John W. Eaton wrote:
> > ...
> > But in other cases, more changes are needed, or we have to accept different
> > behavior.  For example we currently have things like this
> > 
> >   std::string val = args(0).string_value ();
> > 
> >   if (! error_state)
> >     {
> >       // normal processing...
> >     }
> >   else
> >     error ("foobar: first argument must be a character string");
> > 
> > With the change to have the error function throw an exception, the
> > octave_value::string_value extractor will throw an error and so the
> > subsequent more useful message will not appear.  I think in these cases, the
> > fix is to write
> > 
> >   if (! args(0).is_string ())
> >     error ("foobar: first argument must be a character string");
> > 
> >   // normal processing
> > 
> > But there are other cases of extracting values that are not as clear and may
> > need more work.
> 
> What about providing
> 
> #define SOME_MACRO(code, informative_error_message) \
> ...

Death to macros!

In this case it's not so onerous to do

   try
     {
        std::string val = args(0).string_value ();
     }
   catch (invalid_value& e)
     {
        error ("foobar: first argument must be a character string");
     }

In general, replacing if(! error_state) with try-catch blocks is not
that complicated, but it will require changing a lot of calling sites.

- Jordi G. H.