this

  
for my $e (@{[ $$n{'y'} ]}) { 
}
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has no possible autovivification. It copies the list within [] and translates to

  
for my $e (@{[ undef ]}) { 
}
[download]

Nota Bene: there is a fundamental difference between \@a and [@a] !

While both are array refs, only the first one keeps a link to @a while the latter is only an anonymous copy.