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Date: Wed, 28 Oct 2015 11:00:53 +0100
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Subject: In a destructor, how to detect if an exception is currently in flight?
From: erik@evanv.nl (Erik van Velzen)

Subject says it all.

I want to make a small "ScopeGuard" library for exception-safe
transactions, like the following:

    $scope = new ScopeGuard;

    $scope->onSucces(function() { logTransactionOne(); });
    $scope->onFailure(function() { rollbackTransationOne(); });
    doTransactionOne();

    $scope->onSuccess(function() { logTransactionTwo(); });
    $scope->onFailure(function() { rollbackTransactionTwo(); });
    $scope->onFailure(function() { logFailureOfTransactionTwo(); });
    doTransactionTwo();

    // ... Three Four etc...

So if an exception is thrown the attached onFailure callbacks will be
executed, if the scope is exited through a return however the success
callbacks will be executed.

This requires me to know in ScopeGuard::__destruct() if the scope was
left normally or due to an exception.

The code in https://github.com/php/php-src/blob/master/Zend/zend_objects.c#L135
(line 135) seems to prevent me from knowing that information, because
the exception is temporarily removed from the globals and put in a
local variable.

Is there any way to detect if an exception is currently in flight?

(I've asked this same question on SO last week:
http://stackoverflow.com/questions/33199997/in-destruct-how-can-you-see-if-an-exception-is-currently-in-flight)