The Right Approach to Exceptions

[deadalnix]

Le 20/02/2012 20:27, Jonathan M Davis a écrit :
> On Monday, February 20, 2012 11:15:08 H. S. Teoh wrote:
>> On Mon, Feb 20, 2012 at 01:52:15PM -0500, Jonathan M Davis wrote:
>> [...]
>>
>>> So, instead of
>>>
>>> catch(SpecificException1 e)
>>> {
>>>
>>> //use fields specific to this exception to do whatever you need to do
>>>
>>> }
>>> catch(SpecificException2 e)
>>> {
>>>
>>> //use fields specific to this exception to do whatever you need to do
>>>
>>> }
>>> catch(GenericException e)
>>> {
>>>
>>> //handle the generic exception as best you can given the lack of
>>> //a specific one
>>>
>>> }
>>>
>>> you end up with something effectively along the lines of
>>>
>>> catch(GenericException e)
>>> {
>>>
>>> if(/* e is SpecificException1 */)
>>> {
>>> //use fields specific to this exception to do whatever you need to do
>>> }
>>> else if(/* e is SpecificException2 */)
>>> {
>>> //use fields specific to this exception to do whatever you need to do
>>> }
>>> else
>>> {
>>> //handle the generic exception as best you can given the lack of
>>> //a specific one
>>> }
>>>
>>> }
>>
>> [...]
>>
>> I think what Andrei wants to do is more along these lines:
>>
>> catch(Exception e) {
>> writeln(formatLocaleString(e.fmt, e.data));
>> }
>>
>> I think there's some merit to this idea. However, I'm still unsure about
>> storing stuff in a Variant.
>
> Except that if you're not printing out the message, if all of the data is in
> e.data as a variant, then you _do_ end up with code like I gave. The variant
> is a bad idea for anything trying to actually handle the exception rather than
> just print out a message.
>

Have you considered this : 
http://forum.dlang.org/thread/jhos0l$102t$1@digitalmars.com?page=25#post-jhtus4:2416tp:241:40digitalmars.com

>> That's why I proposed to use runtime reflection to scan the exception
>> object for applicable fields. Then you get the best of both worlds: the
>> message formatter doesn't need to know what the fields are, and you get
>> full compile-time type checking for catching code that directly accesses
>> the fields.
>
> That would certainly be better.
>
> - Jonathan M Davis

This is way better than Variant[string], but unimplemented ATM.