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Date: Mon, 25 Mar 2013 18:16:33 +0100
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Subject: Remove support for cloning generators
From: nikita.ppv@gmail.com (Nikita Popov)

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Hi internals!

Now that we're in the beta phase I want to put some finishing touches on
the generators implementation. The first thing I'd like to do is remove
support for cloning generators. There are a few reasons for this:

a) The cloning basically works, but the implementation is rather fragile
and easy enough to break. I just had another look at the code and found two
new ways to make it segfault. I could fix those issues, but I'm pretty sure
that they are not the only bugs in there (that's in the nature of that
code).

b) Especially if objects are involved, the cloning can result in weird
behavior. E.g. if a generator is cloned that makes use of an SplStack,
after cloning both generators will make use of the same stack, which makes
little sense. Just cloning all objects instead of just adding a ref doesn't
make sense either, because cloning would be the wrong thing to do for
objects passed as arguments. One would basically have to clone only objects
created inside the generator, or something like that, which is not
technically possible.

c) Most importantly, there is very little use for the cloning. At first I
thought it would be nice to use cloning in order to implement forking when
using coroutines as a means of multitasking, but this doesn't really work
well due to b). Apart from that I can think of no use for cloning at all.

Patch for removing cloning is here:
https://github.com/nikic/php-src/commit/805b244d8f106431f01b5c013d4e66f9bb88d09b

If no one objects I'll commit it sometime soon.

Thanks,
Nikita

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