Learning Perl Objects, References amp;amp; Modules [Electronic resources] نسخه متنی

11.4 Using AUTOLOAD for Accessors

Chapter 9 showed how to create color
and set_color to get and set the color of an
animal. If you had 20 attributes instead of one or two, the code
would be painfully repetitive. However, using an
AUTOLOAD method, you can construct the nearly
identical accessors as needed, saving both compilation time and
wear-and-tear on the developer's keyboard.

Use a code reference as a closure
to do the job. First, set up an AUTOLOAD for the
object and define a list of hash keys for which you want trivial
accessors:

sub AUTOLOAD {
my @elements = qw(color age weight height);

Next, you'll see if the method is a getter for one
of these keys, and if so, install a getter and jump to it:

our $AUTOLOAD;
if ($AUTOLOAD =~ /::(\w+)$/ and grep $1 eq $_, @elements) {
my $field = ucfirst $1;
{
no strict 'refs';
*{$AUTOLOAD} = sub { $_[0]->{$field} };
}
goto &{$AUTOLOAD};
}

You need to
use ucfirst because you named the method
color to fetch the hash element called
Color. The glob notation here installs a wanted
subroutine as defined by the coderef closure, which fetches the
corresponding key from the object hash. Consider this part to be
magic that you just cut and paste into your program. Finally, the
goto construct jumps into the newly defined
subroutine.

Otherwise, perhaps it's a setter:

if ($AUTOLOAD =~ /::set_(\w+)$/ and grep $1 eq $_, @elements) {
my $field = ucfirst $1;
{
no strict 'refs';
*{$AUTOLOAD} = sub { $_[0]->{$field} = $_[1] };
}
goto &{$AUTOLOAD};
}

If it is neither, death awaits:

  die "$_[0] does not understand $method\n";
}

Again, you pay the price for the
AUTOLOAD only on the first hit of a particular
getter or setter. After that, a subroutine is now already defined,
and you can just invoke it directly.