try..catch..pass..finally Was: DMD 0.148 - scope guard

[Regan Heath]

On Tue, 28 Feb 2006 06:34:00 +0000 (UTC), Tom Johnson  
<Tom_member at pathlink.com> wrote:
>> I'd say add another option to try..catch..finally paradigm.
>>
>> -S.
>
> Seconded.  For more fun, next we can debate whether the syntax should be:
>
> 1.  try..pass..catch..finally
> 2.  try..catch..pass...finally
> 3.  try..catch..finally..pass

No, on_scope gives us more than try/catch/finally. Let me try this another  
way.

"catch" from try/catch/finally allows:
  - you to execute a static/pre-defined set of code in the event that there  
is a failure in the current scope.

"finally" from try/catch/finally allows:
  - you to execute a static/pre-defined set of code at the exit of the  
current scope in all cases.

Compare that to:

on_scope_failure allows:
  - you to add one or more sets of code, at the points at which they become  
required, to the list of things to execute in the event of a failure.

on_scope_exit allows:
  - you to add one or more sets of code, at the points at which they become  
required, to the list of things to execute at the exit of the scope in all  
cases.

To achieve the same thing that on_scope gives with try/finally requires  
you to store state somewhere to indicate which parts of the finally block  
to execute, or, it requires that you define several finally blocks and  
nest them. Both of those options are no where near as neat as on_scope.

I'm honestly baffled that people can't see the difference.

Regan