Re: Using exceptions in the core

[John W. Eaton]

On 10/07/2015 02:06 AM, Olaf Till wrote:
> On Tue, Oct 06, 2015 at 11:15:00PM -0400, Mike Miller wrote:
> > I still think it's a little weird to say "convert to a string for me,
> > here's an error message just in case", is there really no better way?
>
> What occured to me now, though maybe a mad idea and much more work, is
> overloading as ..._value (..., bool& err) (somehow avoiding to have
> the same signature as the existing functions), and for this variant
> not to throw, but to set 'err' to true. This wholly avoids the
> try/catch, leaves the user the resposibility to check 'err', but only
> in the cases where he explicitely requested it by using this
> overloaded variant.

So you would have to write

  bool err = false;

  value_type val = arg.value_extractor (err);

  if (err)
    error ("error message here");

I see that as no better than either

  value_type val;

  try {
    arg.value_extractor ();
  } catch {
    error ("error message here");
  }

or

  value_type val = arg.value_extractor ("error message here");

The last option is certainly more concise.

jwe