Now What?

So now we have a cache object...  What can we do with it?
Well the first thing to mention is what not to do with it: don't attempt recursive inspection of the object with something like Data::Dumper or the debugger's x command.  The deeply recursive nature of the underlying object will cause such inspection to run for ever (or OOM, whichever comes first).

The cache appears as a hashref, with entries for every package mentioned in the Packages files as AptPkg::Cache::Package objects.  These objects also appear as hashrefs of the package attributes and so on.  Here are some examples:

    $cache->{perl}{CurrentVer}{VerStr}
    $cache->{perl}{VersionList}[0]{VerStr}

Those values being strings representing the currently installed version of perl, and the newest available version.

Of course a diagram might make this all a bit clearer...