理清这4个模式需要了解perl参考

Question

I really really don't undertand perl hash. I have been reading perl doc but not able to completely get perl reference.

For a prime example, can you please tell me the difference between below?

 @{$table}{$item}
 @{$table{$item}}
 %{$table}{$item}
 %{$table{$item}}

Or is there some general rule that I am missing from not able to decipher these?

Please point me to right direction. I have been reading perldoc.perl.org..

Answer 1

Just replace the reference-producing block ( {... } ) with an identifier to get a better sense of what you have.

• @{$table}{$item}
  • Akin to @name{$item}
  • Array slice of the array referenced by $table
  • Can also be written as $table->@{$item}
  • There's no point to using a slice when there's only one item returned by the index expression. Should be ${$table}{$item} or $table->{$item} .
• @{$table{$item}}
  • Akin to @name
  • Array referenced by $table{$item}
  • Can also be written as $table{$item}->@*
• %{$table}{$item}
  • Akin to %name{$item}
  • Key-value hash slice of the hash referenced by $table
  • Can also be written as $table->%{$item}
• %{$table{$item}}
  • Akin to %name
  • Hash referenced by $table{$item}
  • Can also be written as $table{$item}->%*

See

• Perl Dereferencing Syntax
• perlreftut
• perllol
• perldsc
• perlref