TryElseExpression DIP

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On Monday, 5 September 2016 at 18:27:44 UTC, ag0aep6g wrote:
> Can you point out how this is different from (and better than)
>
>     try { do_a_thing(); depends_on_success_of_thing(); }
>     catch (...) { ... }
>     finally { ... }
>
> ?

On Monday, 5 September 2016 at 18:27:52 UTC, arturg wrote:
> hm, isn't this similar/same as the python version?
>
>   try{
>       doSomething();
>
>       scope(success) "if no Exception thrown".writeln;
>   }
>   catch(Exception e)
>   {
>        ...
>   }

In this case, the catch block will catch both errors from 
do_a_thing and depends_on_success_of_thing. The places where this 
sort of pattern is most useful are where you don't want to handle 
errors in depends_on_success_of_thing at all, because to have 
thrown an error is very unexpected behavior.

Granted scenarios like that are uncommon, but the most important 
reason for using the separate `else` scope is to help reduce 
programmer error because they forgot that the error handling in 
the catch block will break something when it was entered because 
depends_on_success_of_thing failed.

There's also the matter of readability and cleanliness. It is (in 
my opinion, at least) an intuitive and concise way to handle a 
not-uncommon case.