Programming Perl, 4th Edition

Composition, Access, and Printing of More Elaborate Records

Here is a record with six disparate fields:

$rec = {
    TEXT      => $string,
    SEQUENCE  => [ @old_values ],
    LOOKUP    => { %some_table },
    THATCODE  => \&some_function,
    THISCODE  => sub { $_[0] ** $_[1] },
    HANDLE    => \*STDOUT,
};

The TEXT field is a simple string, so you can just print it:

print $rec–>{TEXT};

SEQUENCE and LOOKUP are regular array and hash references:

print $rec–>{SEQUENCE}[0];
$last = pop @{ $rec–>{SEQUENCE} };

print $rec–>{LOOKUP}{"key"};
($first_k, $first_v) = each %{ $rec–>{LOOKUP} };

THATCODE is a named subroutine and THISCODE is an anonymous subroutine, but they’re invoked identically:

$that_answer = $rec–>{THATCODE}–>($arg1, $arg2);
$this_answer = $rec–>{THISCODE}–>($arg1, $arg2);

With an extra pair of braces, you can treat $rec–>{HANDLE} as an indirect object:

print { $rec–>{HANDLE} } "a string\n";

If you’re using the IO::Handle module, you can even treat the handle as a regular object:

use IO::Handle;
$rec–>{HANDLE}–>autoflush(1);
$rec–>{HANDLE}–>print("a string\n");