I have a project that currently uses Guzzle (which is loaded [as a .phar] by an explicit "require_once" in a bootstrap file).
I have been trying to add the AWSSDKforPHP from Amazon, so that I can easily handle uploads to Amazon S3. Unfortunately, when I try to include the package (also packaged as a .phar file), PHP throws a nasty error:
PHP Fatal error: Cannot redeclare class Symfony\\Component\\ClassLoader\\UniversalClassLoader in phar:///usr/share/php/AWSSDKforPHP/aws.phar/vendor/symfony/class-loader/Symfony/Component/ClassLoader/UniversalClassLoader.php on line 62
I have already turned off (completely) APC, as I've seen APC cause some require/include headaches before.
I doubt that PHP would have such an awkward limitation of only being able to include a package with a dependency once. ... But I could be wrong.