[PEPr] Comment on Caching::phpfastcache

After looking at the code, I agree with Bertand. This class is doing too
much. For example, emailing error messages does not belong in a cache
library.

There is definitely room in PEAR for a cache library, but the code needs to
be split into multiple reusable classes rather than one monolithic static
class.

Serializing cache data is potentially a security issue as a vulnerability
in any backend now has the potential to execute code on the server.

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http://pear.php.net/pepr/pepr-proposal-show.php?id=692