Sometimes you *don't* want circular checking

I use the nifty Data::Rmap to "flatten" DateTime objects into strings so they can be exported to JSON and handled outside Perl. But due to circular checking in Data::Rmap, this:

$ perl -MData::Rmap=:all -MData::Dump \
-e'$d = DateTime->now; $doc = [$d, $d];
rmap_ref { $_ = $_->ymd if UNIVERSAL::isa($_, "DateTime") } $doc;
dd $doc'

produces something like this:

["2010-10-01", ...unconverted DateTime object...]

For now I work around this by defeating Data::Rmap's circular checking, though I wonder if there's a better way.

$ perl -MData::Rmap=:all -MData::Dump \
-e'$d = DateTime->now; $doc = [$d, $d];
rmap_ref { $_[0]{seen} = {}; $_ = $_->ymd if UNIVERSAL::isa($_, "DateTime") } $doc;
dd $doc'

will correctly produce:

["2010-10-01", "2010-10-01"]