my %quick_allow = map { $_ => 1 } @allow_users;

[download]

means 

my @anon;
for (@allow_users) {
   push @anon, do { $_ => 1 };
}
my %quick_allow = @anon;

[download]

which does 

my %quick_allow;
for (@allow_users) {
   $quick_allow{$_} = 1;
}

[download]
my %ALL_USER_GROUPS = (
                    23 => [ qw( g1  g4 ) ],
                    13 => [ qw( g3  g5 ) ],
                    );

[download]

is a HoA. It could have been written 

my %ALL_USER_GROUPS = (
                  # key   value
                  # ----- ---------------
                    '23', [ 'g1', 'g4' ],
                    '13', [ 'g3', 'g5' ],
                    );

[download]

=> implies a key-value relationship, and qw() just saves typing and clutter.

When dereferencing complex data structures, where do I start? How do I know when a reference ends and when to add another curly brace or sigil?

Deconstruct it one level at a time. 

# At the outmost level, you have a list of groups stored in a hash.
# List the keys (group ids) and fetch the corresponding value (group m
+embers).
for my $gid ( keys %ALL_USER_GROUPS )
   my $members = $ALL_USER_GROUPS{$gid};

   print("Group: $gid\n");

   # Now we want to dump the list of group members.
   for my $member (@$members) {
      print("Member: $member\n");

      # That's it.
   }

   print("\n");
}

[download]

Once you got that far, you can play with the formatting. For example, you could replace the inner loop with a join to print all the members on one line: 

for my $gid ( keys %ALL_USER_GROUPS )
   my $members = $ALL_USER_GROUPS{$gid};
   print("Group:   $gid\n");
   print("Members: ", join(' ', @$members), "\n");
   print("\n");
}

[download]

In reply to Re: Need help with perl syntax. by ikegami
in thread Need help with perl syntax. by Anonymous Monk

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