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Date: Mon, 24 Dec 2012 07:09:36 -0500
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To: Tjerk Anne Meesters <datibbaw@php.net>
Cc: Stas Malyshev <smalyshev@sugarcrm.com>, Nikita Popov <nikita.ppv@gmail.com>, 
	PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=14dae9cdc6c128b32904d19812fa
Subject: Re: [PHP-DEV] Adding Generator::throw()
From: ircmaxell@gmail.com (Anthony Ferrara)

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Tjerk,

I've been hearing this argument from time to time and I don't understand
> it; aren't exceptions created with the sole purpose of (error) flow
> control?
>
> If so, then how can "exceptions for flow control" and "very bad idea" be
> mentioned in the same sentence unless there are particular bad use cases
> that are implicitly referred to when saying this?
>
> If not, then perhaps my understanding of exceptions needs a spring cleaning
> :)


Correct, Exceptions aren't supposed to be used for flow control.

However, this isn't about flow control. This is about throwing the
exception in the proper context. With generators and coroutines, the code
that throws the exception may not actually be a child of the code that
called it (from the stack's perspective). Therefore, adding
Generator::throw() simply allows for throwing the exception in the proper
stack frame (the framew that called the original code).

For an example of how this would be useful, read this *awesome* post about
coroutines:
http://nikic.github.com/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html

Anthony

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