DMD 0.148 - scope guard

[Dawid Ciężarkiewicz]

James Dunne wrote:
> I don't like the words 'success' and 'failure' used all over the place.

Yes. I have to agree they are little missused. Changing them to "pass" as
success, "fail"/"catch" as "failure" and "default" as exit is good idea.

> void LongFunction()
> {
>      scope (State save = UIElement.GetState())
>      catch {
>          UIElement.SetState(Failed(save));
>      }
>      pass {
>          UIElement.SetState(save);
>      }
>      body {
>          ... lots of code ...
>      }
> }
> 
> This way, it looks like a function contract, except it applies to any
> scope.  The catch block is reused but only for purposes of noting that
> there was an exception caught.  The pass block is quite simply the
> 'else' to the catch block, and should happen only if no exceptions were
> caught.  Furthermore, there could be a general 'exit' block.
> 
> One could add as many of these blocks as necessary, and the compiler
> will guarantee to call them in order of definition, much like the
> original solution but not requiring one to think backwards.
> 
> bool LongFunction()
> {
>      bool  passed = false;
> 
>      scope (State save = UIElement.GetState())
>      catch { UIElement.SetState(Failed(save)); writef('0'); }
>      pass { UIElement.SetState(save); writef('1'); }
>      pass { passed = true; writef('2'); }
>      body {
>          ... lots of code ...
>      }
>      exit { writef('3'); }
> 
>      return passed;
> }
> 

IMHO now it looks overcomplicated. You are explicitly declaring new scope
using body {} . This is for what whole idea was invented - to prevent it.

Using "catch" keyword is missleading. Keyword scope (expr.) works now as try
{ expr. } . And I have to say that I needed to read this code few times to
understand it. It looks for me as reinventing try { } catch { } finally {}
way of handling exceptions. Sorry, but I don't like it.