dolfin team mailing list archive

[Florian Rathgeber <florian.rathgeber@xxxxxxxxxxxxxx>]

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On 02.08.2010 18:50, Garth N. Wells wrote:
> On Mon, 2010-08-02 at 10:33 +0200, Anders Logg wrote:
>> On Sun, Aug 01, 2010 at 06:35:22PM +0100, Garth N. Wells wrote:
>>> On Sun, 2010-08-01 at 12:40 +0200, Florian Rathgeber wrote:
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>>>> Hi,
>>>>
>>>> When using GenericTensor::down_cast() for a tentative down cast it would
>>>> be helpful if it would throw std::bad_alloc (as any dynamic_cast would
>>>> do)
>>>
>>> Do you mean std::bad_cast?
>>>
>>>> instead of invoking dolfin::error. Currently you would have to catch
>>>> std::runtime_error and check what() to distinguish a failed cast from
>>>> another dolfin::error, which is pretty inconvenient. Is there a specific
>>>> reason why it is implemented this way?
>>>>
>>>
>>> Not really.
>>>
>>> It's not too clear to me what you'd like. Would you prefer that
>>> down_cast doesn't throw an error, but leave it up to the programmer to
>>> check that a cast was successful, or just that DOLFIN catch a
>>> std::bad_cast and print more information before throwing an error?
>>
>> I think the best would be if DOLFIN caught the error, then wrote an
>> informative message (since it knows exactly what went wrong) and then
>> threw bad_cast.
>>
> 
> Looks like there isn't much that can be done - std::bad_cast is only
> thrown when casting references, not pointers (as we do internally). From
> what I've read, our way of checking for a null pointer is correct.

If down_cast() were implemented as casting the reference directly,
dynamic_cast would throw std::bad_cast if it fails.

The check for the null pointer is correct, my point is that in this case
not a std::runtime_error should be thrown (which happens by calling
dolfin::error), but instead the message should be printed e.g. by
dolfin::warning and then a std::bad_cast thrown. That was Anders'
suggestion if I got that right.

In that way down_cast() could be used as a tentative cast which is not
really possible if it throws the same exception that could be caused by
and DOLFIN error.

Florian

> Garth
> 
>> --
>> Anders
> 
> 
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