Every once in someone likes to argue that PEAR is all fugly PHP4 code and why you should not use it, and instead go and use another framework or component library. Most of those people also say that they looked at or used PEAR x years ago and then act all surprised when someone else disagrees.
In related (BC) news, most people probably read my blog because of Zend Framework, and I remember that one of the reasons I sold my clients on Zend Framework was a supposedly backward compatibility and clean API. Well, a couple years later one knows it's not all that and since another BC break was argued today on one of the mailing lists and the project lead said I spread fud, I felt l needed to write something on the topic.
Facts first.
A small history of PEAR.
I don't know how old exactly PEAR is, but the manual is copyrighted since 2001 and none of the other current frameworks have been around eight — almost nine — years.
Because PEAR has been around much longer, we also have more older code than any of those PHP5-only frameworks. In comparison, Zend Framework's first stable was release in June, 2007, almost six years later.
Major versus minor releases.
A package' version consists of x.y.z.
The rules are as follow:
- A BC break (see below) — increment x, and set y and z to 0.
- Adding a new feature — keep x, increment y and set z to 0.
- Fixing a bug — keep x and y, but increment z.
When someone refers to a major release in PEAR's context (and a lot of other projects such as Zend Framework, Solar and ezComponents follow this), it's one with a change in x. :-)
What is backward compatibility?
Backward compatibility, or BC, describes that a component, package or library preserves compatibility with an older versions.
Because programming itself and developers tend to evolve, PEAR tries to keep BC in all minor versions, but allows you to break compatibility to an earlier version with a new major release.
The exception to the rule is that you may break BC during alpha and beta releases before the package reaches a stable 1.0.0. Once a 1.0.0 is reached, BC may not be broken — for whatever reason.
PHP4?
Because PEAR aims to provide BC all the way, BC includes the PHP version when the package was first released. Which in turn means that of course you may make the code compatible to a later PHP release, but not without breaking compatibility to the initial release.
If you followed the above, you understand the reason why for example there is a Mail_Queue and (a soon to be) Mail_Queue2, or more importantly: why the Mail_Queue release in 2009 is still compatible to PHP4. Even though PHP4 EOL'd a while ago.
The first Mail_Queue package was released in September of 2002, the 1.0.0 stable release followed in December of the same year. Because its 1.0.0 was compatible with PHP4, we keep it backwards compatible with PHP4 until we release Mail_Queue2-0.1.0.
A principal
A lot of people argue that with the official end of life of PHP4, one should break BC anyway. But here is why you should not.
Even though we all love to use PHP5, there is still a lot of PHP4 in the enterprise. And like it or not, many of those apps use PEAR, and not your funky PHP5 framework.
How do you keep so-called necessary and unnecessary BC breaks apart? From another point of you (which is not your own), there is always a necessary BC break to fix implement something else.
Because there is no such thing as small or acceptable BC breaks. There are BC breaks or there are none, it's one of those things that is black and white.
BC in other frameworks
I know for a fact that ezComponents is very strict on BC. I cannot comment on Solar or Symfony, but at least in Solar's case, I'm assuming that adhere to BC as well since a some former PEAR developers are active and they also follow the PEAR Coding Standard in many respects.
Zend Framework?
A friend of mine said that if Zend Framework really kept BC, we would at 10.0.0 and not on 1.9.3.
Reasons why Zend Framework likes to break BC, even though it advertises full BC:
No versioning per components but per framework.
Missing peer review and QA leads to unstable code in a so-called stable release. (Which in turn also fakes the stability of the entire framework since it suggests that a component that was added a couple weeks ago is as stable as a component added in 2007.)
Because it fixes an "issue". (Biggest WTF of them all.)
The issue in question, I'm not even sure what they were trying to fix. Supposedly some developers found it too hard or did not understand how to write an adapter for Zend_Db and someone committed a fix in the 1.9 tree/branch and apparently it was OK to break BC because it was the easier way out.
I haven't updated some projects since late 1.8.x because of these BC breaks because no one can tell me what the issue is and I don't have a day to debug my application to figure out where and how it breaks. This is annoying as hell, especially since they are supposed to be tailored to the business.
On a side-note, I know of a couple components (e.g. Zend_Session) which really deserve (!) a BC break and don't get one until 2.0. And I totally get why, but why is it OK in some cases? All BC breaks fix issues!
(Btw, as I finish this post, I see an email to zf-contributor@ in my inbox where someone considers pulling the 1.9.3 release (because it obviously breaks BC). Guess I didn't spread that much FUD after all.)