[optional] How to make boost::optional throw if trying to access uninitialized value

[dariomt]

Hi list,

I've seen in the docs that boost::optional asserts if you try to access an uninitialized value.

Is it possible to make it throw an exception instead? Even in release mode?

TIA


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[Josh Kelley-2]

On Thu, Jul 9, 2009 at 1:13 PM, <dariomt@...> wrote:
> I've seen in the docs that boost::optional asserts if you try to access an uninitialized value.
>
> Is it possible to make it throw an exception instead? Even in release mode?

You can change BOOST_ASSERT's behavior by defining
BOOST_ENABLE_ASSERT_HANDLER.  See
http://www.boost.org/doc/libs/1_39_0/libs/utility/assert.html for
details.

boost/assert.hpp can be included multiple times in a single
translation unit, so if you want boost::optional to throw exceptions
but other parts of Boost to still assert, you can define
BOOST_ENABLE_ASSERT_HANDLER immediately before including
boost/optional.hpp and undefine it immediately afterward.

Josh Kelley
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[dariomt]

Josh Kelley <joshkel <at> gmail.com> writes:

>
> On Thu, Jul 9, 2009 at 1:13 PM, <dariomt <at> gmail.com> wrote:
> > I've seen in the docs that boost::optional asserts if you try to access an
uninitialized value.

> >
> > Is it possible to make it throw an exception instead? Even in release mode?
>
> You can change BOOST_ASSERT's behavior by defining
> BOOST_ENABLE_ASSERT_HANDLER.  See
> http://www.boost.org/doc/libs/1_39_0/libs/utility/assert.html for
> details.
>
> boost/assert.hpp can be included multiple times in a single
> translation unit, so if you want boost::optional to throw exceptions
> but other parts of Boost to still assert, you can define
> BOOST_ENABLE_ASSERT_HANDLER immediately before including
> boost/optional.hpp and undefine it immediately afterward.
>
> Josh Kelley
>

Thanks for the info!

I think it is not possible to have a specific boost::assertion_failed handler
for boost::optional and other handlers for other assertion failures in other
places, right?

That would mean that the exception I throw from the handler cannot mention the
fact that I am accessing an uninitialized value in a boost::optional.

Maybe I should create my own my::safe_optional based on boost::optional but
checking for uninitialized access.

Any ideas?


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[Anders Dalvander-3]

dariomt@... wrote:

> Thanks for the info!
>
> I think it is not possible to have a specific boost::assertion_failed handler
> for boost::optional and other handlers for other assertion failures in other
> places, right?
>
> That would mean that the exception I throw from the handler cannot mention the
> fact that I am accessing an uninitialized value in a boost::optional.
>
> Maybe I should create my own my::safe_optional based on boost::optional but
> checking for uninitialized access.
>
> Any ideas?
>  

You could create your own functions for this:

template <typename T>
T const& safe_get(boost::optional<T> const& opt)
{
   if (!opt)
      throw some_exception();
   return *opt;
}

template <typename T>
T& safe_get(boost::optional<T>& opt)
{
   if (!opt)
      throw some_exception();
   return *opt;
}

Regards,
Anders Dalvander

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