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eval { $yaml_class->import( 'Dump'); 1; }
  or croak( "Can't find Dump in $yaml_class\n" );

Package::Stash->new( $yaml_class )->has_symbol( '&Dump' )
  or croak( "Can't find Dump in $yaml_class\n" );

my $Dump = $yaml_class . "::Dump";
[... later in the code ...]
my $var = eval { &$Dump(...) } or croak( "bad return or Dump not imple
+mented\n" );