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use feature qw( say );
use B qw( );
...
my ($f,$g) = (333,"xyz");
say B::class(B::svref_2object(\$f));
say B::class(B::svref_2object(\$g));

IV
PV

use feature qw( say );
use B qw( );
...
"".$_;
$_ = undef;
say B::class(B::svref_2object(\$_));

PVIV