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Date: Wed, 5 Nov 2014 21:20:14 +0100
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Subject: Thresholds of backwards compatibility breaks
From: florian@margaine.com (Florian Margaine)

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Hi list,

I'd like to introduce thresholds of backwards compatibility breaks, i.e.
maximum numbers of allowed BC breaks per version.

Lester's mail from a couple days ago had me thinking about the BC breaks
that occur now and then in all the RFCs or all the mails I see these days.
Now, take what I say with a grain of salt, as I've only recently been
involved in this mailing list, as well as in php-src development.

Let me explain my reasoning.

To allow the users of PHP to upgrade their versions, and enjoy the new
features, as well as the security fixes, the least number of BC breaks
should get in the new released versions. That is because a BC break can
lead to many hours of a codebase adaptation, hours that many companies
don't want to pay for if the benefits are minimal.

However, to allow us to evolve the language, BC breaks are a necessary evil.

Another issue is the short timeline of security fixes for the versions. PHP
5.4 will have a total lifetime of 3 years, a very short one for many
people. I'm not advising to increase this timeline, just saying that it
gets in the equation of my discussion.

To mitigate the issue of BC breaks, I think introducing the concept of
thresholds would greatly help the PHP adoption, and mostly upgrades of PHP
versions. If people know that a limited amount of work is going to be
needed when upgrading a PHP version, the upgrades should be done more often.

For example, the following thresholds could be used:

- major BC break: major versions only. 5 major BC breaks allowed per major
version.
- minor BC break:
  - minor versions: 5 minor BC breaks allowed.
  - patch versions: 1 BC break allowed.

Thoughts? Am I thinking too much? Is this idea unfeasible? Is it a good
idea?

Regards,
-- 
Florian Margaine

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