This is a bit embarrassing. I thought I understood dereferencing, but in glancing at a coworke'rs code, I stumbled across an edge case I don't understand. He was using a ternary operator, but instead using it to choose what he's assigning from, he used it to choose what he's assigning to:

# assigning from:
my $foo = $bar ? $baz : $quux;

# assigning 'to
push @{ $row->{close_time} ? \@closed : \@open }, $row;
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That surprised me, but it seems reasonable. But then he also pointed out that taking a reference to the arrays is not necessary:

push @{ $row->{close_time} ? @closed : @open }, $row;

I thought that @{} would dereference the contained expression. The following script further illustrates my confusion:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my ( @open, @closed );

my $open = 1;
push @{ $open ? @open  : @closed }  => 'boo!';
push @{ $open ? \@open : \@closed } => 'boo!';
print Dumper( \@open );

push @{ @{ @{ @{ @{@open} } } } } => ['bar'];
print Dumper(\@open);
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That prints:

$VAR1 = [
          'boo!',
          'boo!'
        ];
$VAR1 = [
          'boo!',
          'boo!',
          [
            'bar'
          ]
        ];
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I've been using @{} and similar constructs for so long that I can't even remember where they are documented. perlref says:

Anywhere you'd put an identifier (or chain of identifiers) as part of a variable or subroutine name, you can replace the identifier with a BLOCK returning a reference of the correct type. In other words, the previous examples could be written like this:

    $bar = ${$scalarref};
    push(@{$arrayref}, $filename);
    ${$arrayref}[0] = "January";
    ${$hashref}{"KEY"} = "VALUE";
    &{$coderef}(1,2,3);
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That suggests that the block is supposed to return a reference, but clearly it's not required Is this documented behavior?