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To: internals@lists.php.net,Markus Malkusch <markus@malkusch.de>, internals@lists.php.net
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Subject: Re: Throwable::addSuppressed()
From: me@stephencoakley.com (Stephen Coakley)

On 07/28/2015 04:51 PM, Markus Malkusch wrote:
> Hi PHP
>
> So I read that there's this Throwable interface coming. Great! How about
> extending it with one further method:
>
> void Throwable::addSuppressed(Throwable exception)
>
> Semantic is the same as Java's Throwable.addSuppressed()¹.
>
> Why? Well consider a code fragment which wants to close a resource
> during an exception:
>
> } catch (Exception $e1) {
>      try {
>          $resource->close();
>          throw $e1;
>
>      } catch (ResourceException $e2) {
>          // The information about $e2 is lost.
>          throw $e1;
>      }
> }
>
> Currently PHP has no method to propagate both $e1 and $e2. With
> Throwable::addSuppressed() $e2 could be added as a suppressed exception
> to $e1:
>
> } catch (Exception $e1) {
>      try {
>          $resource->close();
>
>      } catch (ResourceException $e2) {
>          e1->addSuppressed($e2);
>
>      }
>      throw $e1;
> }
>
> To make this information useful (for e.g. a logger) there's one further
> method needed:
>
> Throwable[] Throwable::getSuppressed()
>
> So PHP, what do you think, might a RFC find acceptance?
>
> Best wishes
> Markus Malkusch
>
> [1]:
> http://docs.oracle.com/javase/8/docs/api/java/lang/Throwable.html#addSuppressed-java.lang.Throwable-
>

Interesting thought, but how is this different than including a previous 
throwable and throwing a new, more descriptive exception?

} catch (Exception $e1) {
      try {
          $resource->close();
      } catch (ResourceException $e2) {
          // Pass in $e2 as the previous exception in the chain.
          throw new ResourceFailedException($e1->getMessage(), 
$e1->getCode(), $e2);
      }
}

What you're describing doesn't seem like a common use case.

Also, this is pretty nitpicky, but the above code might fit better with 
a finally block when closing resources:

try {
     // Do something with $resource here...
} finally {
      $resource->close();
}

-- Stephen Coakley