This is a repost of an email that I sent to PHP internals as a reply to:
And since you're targetting[sic] the next major release, BC isn't an issue.
This sort of blanket statements that "Backwards Compatibility is not an issue" with a new major version is extremely unwarranted. Extreme care should be taken when deciding to break Backwards Compatibility. It should not be "oh we have a major new version so we can break all the things"™.
There are two main types of breaking Backwards Compatibility:
The obvious case where running things trough
php -linstantly tells you your code no longer works. Bugs like the two default cases, fall in this category. I have no problem with this, as it's very easy to spot the difference (In the case of allowing multiple "default" cases, it's a fricking bug fix too).
Subtle changes in how PHP behaves. There is large amount of those things currently under discussion. There is the nearly undetectable change of the "Uniform Variable Syntax", that I already wrote about, the current discussion on "Binary String Comparison", and now changing the behaviour on
>>in a subtle way. These changes are not okay, because they are nearly impossible to test for.
Changes that are so difficult to detect, mean that our users need to re-audit and check their whole code base. It makes people not want to upgrade to a newer version as there would be more overhead than gains. Heck, even changing the
$in front of variables to
£is a better change, as it's immediately apparent that stuff changed. And you can't get away with "But Symfony and ZendFramework don't use this" either, as there is so much code out there
As I said, the first type isn't much of a problem, as it's easy to find what causes such Backwards Compatibility break, but the second type is what causes our users an enormous amount of frustration. Which then results in a lot slower adoption rate—if they bother upgrading at all. Computer Science "purity" reasons to "make things better" have little to no meaning for PHP, as it's clearly not designed in the first place.
Can I please urge people to not take Backwards Compatibility issues so lightly. Please think really careful when you suggest to break Backwards Compatibility, it should only be considered if there is a real and important reason to do so. Changing binary comparison is not one of those, changing behaviour for everybody regarding
>> is not one of those, and subtle changes to what syntax means is certainly not one of them.
Don't be Evil