I am new in PHP with at most 1 month exp. And I am writing a PHP SDK for a cloud storage service and I am hoping not make any big mistakes so that most my target users (PHP developers) can use this SDK without trouble-shooting.
Now I am worrying about which version the SDK should be based on. PHP 5.3 is good with Namespace feature, and I can see AWS PHP SDK (http://aws.amazon.com/sdkforphp) is based on PHP 5.5. But I think the newer my SDK PHP version is, the less user will be able to use it because of backward compatibility.
So please tell me what is the convension in PHP version supporting? Or a more closed question: Is it a bad idea for my SDK to be based on PHP 5.3?
Thanks to @JohnConde and now I realized the real question should be which is the most used PHP version and it's already answered Which PHP 5 Version is most commonly used?.
I think many things have changed for the better with the new versions of php. Both in terms of resources and in terms of performance. Many fixes were also made. See the changelog: http://us3.php.net/ChangeLog-5.php
Php 5.4 is two times faster What 5.3 (http://www.lornajane.net/posts/2012/proof-that-php-5-4-is-twice-as-fast-as-php-5 -3), the 5.5 is faster than the 5.4 and so on (http://www.lornajane.net/posts/2014/php-5-6-benchmarks).
In terms of features and support for object orientation it is also much better. I recommend using at least version 5.5.9.
I just upgraded two applications that ran with PHP 5.2 and are now with PHP 5.5.9. The effort was not big and the benefits were wonderful. Much faster now... and my very satisfied customers. In general, syntax changes become simpler code. Therefore, the effort was small. The code is much easier to read and future maintenance will be much easier and faster to implement.
I hope this helps!