DIP 1002 (TryElseExpression) added to the queue

[Idan Arye via Digitalmars-d]

On Tuesday, 27 September 2016 at 09:48:42 UTC, Jonathan M Davis 
wrote:
> On Tuesday, September 27, 2016 09:30:10 Dicebot via 
> Digitalmars-d wrote:
>> https://github.com/dlang/DIPs/blob/master/DIPs/DIP1002.md
>>
>> PR: https://github.com/dlang/DIPs/pull/43
>>
>> Abstract:
>>
>> In Python, the try/catch/finally syntax is augmented with an 
>> additional clause, termed else. It is a fantastically useful 
>> addition to the conventional syntax. It works like this:
>>
>> ```
>>      try:
>>          do_something()
>>      except Exception as e:
>>          pass # Runs when an error inheriting from Exception 
>> was
>> raised
>>      else:
>>          pass # Runs when no error was raised
>>      finally:
>>          pass # Runs unconditionally, evaluates last
>> ```
>
> And why not just put the code that would go in the else at the 
> end of the try block? Just like with this proposed else, the 
> code would only run if the preceding code didn't throw any 
> exceptions. This just seems like an attempt to make D more like 
> python rather than to add anything useful.
>
> - Jonathan M Davis

Exceptions thrown in the `else` clause are not caught in the 
catch/expect clauses. This gives you finer grained control:


     try {
         auto f1 = File("f1.txt");
     } catch (ErrnoException) {
         // f1.txt not found? no biggie...
     } else {
         // This won't happen if we can't open f1.txt

         // If we can't open f2 we don't want to catch the 
exception:
         auto f2 = File("f2.txt", "w");

         // Do stuff with f1 and f2
     }

     // This will still happen even if we can't open f1.txt


BTW, if this feature is ever implemented in D, it's important 
that the else clause will continue the try clause's scope.