Programming Perl, 4th Edition

Generating Accessors with Closures

Most accessor methods do essentially the same thing: they simply fetch or store a value from that instance variable. In Perl, the most natural way to create a family of near-duplicate functions is looping around a closure. But closures are anonymous functions lacking names, and methods need to be named subroutines in the class’s package symbol table so that they can be called by name. This is no problem—just assign the closure reference to a typeglob of the appropriate name.

package Person;

sub new {
    my $invocant = shift;
    my $self = bless({}, ref $invocant || $invocant);
    $self–>init();
    return $self;
}

sub init {
    my $self = shift;
    $self–>name("unnamed");
    $self–>race("unknown");
    $self–>aliases([]);
}

for my $field (qw(name race aliases)) {
    my $slot = _ _PACKAGE_ _ . "::$field";
    no strict "refs";          # So symbolic ref to typeglob works.
    *$slot = sub {
        my $self = shift;
        $self–>{$field} = shift if @_;
        return $self–>{$field};
    };
}

Closures are the cleanest hand-rolled way to create a multitude of accessor methods for your instance data. It’s efficient for both the computer and you. Not only do all the accessors share the same bit of code (they only need their own lexical pads), but later if you decide to add another attribute, the changes required are minimal: just add one more word to the for loop’s list, and perhaps something to the init method.