Re: Using exceptions in the core

[John W. Eaton]

On 09/28/2015 10:42 AM, Jordi Gutiérrez Hermoso wrote:
> On Sun, 2015-09-27 at 10:38 +0200, Olaf Till wrote:

> > 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.

I think we also want to avoid adding many try-catch blocks if possible.

In this case, instead of a macro, maybe an in-line function like

  inline std::string
  get_string (const octave_value& arg, const std::string& msg = 
std::string ())
  {
     std::string retval;

     try
       {
          retval = arg.string_value ();
       }
     catch
       {
         if (! msg.empty ())
           error ("%s", msg.c_str ());
         else
           throw;
       }

     return retval;
  }

Then we could just write

  std::string val = get_string (args(0), "foobar: first argument must 
be a character string");

and we would (currently) see something like

  error: octave_base_value::convert_to_str_internal (): wrong type 
argument 'matrix'
  error: foobar: first argument must be a character string

It would probably be good to take this opportunity to modify the 
behavior to either omit the wrong-type argument message, or at least 
clean it up so that it doesn't print the 
"octave_base_value::convert_to_str_internal ()" part.

In any case, this seems cleaner and clearer than having either the 
try-catch block repeated many times or writing

  if (! args(0).is_string ())
    {
      error ("foobar: first argument must be a character string");
      return retval;
    }

  std::string val = args(0).string_value ();

I'm not sure whether I would have this as a simple function or make it a 
method in the otave_value class.  I suppose it could just be an 
overloaded version of the octave_value::string_value method.

jwe