perl 5.10不支持伪散列了阿？［已解决］

perl 5.10不支持伪散列了阿？

请问您的伪散列是什么意思？
$a={a=>b,c=>d};
print keys(%$a);
我用的是5.10 可以得到a，c啊！请指教

Pseudo-hashes: Using an array as a hash

   $struct = [{foo => 1, bar => 2}, "FOO", "BAR"];

   $struct->{foo};  # same as $struct->[1], i.e. "FOO"
   $struct->{bar};  # same as $struct->[2], i.e. "BAR"

http://www.perl.com/doc/manual/html/pod/perlref.html