By not assuming our own class as the default second argument and instead
using the class passed into us, we make our constructor inheritable.
-While we're at it, let's make our constructor a bit more flexible.
-Rather than being uniquely a class method, we'll set it up so that
-it can be called as either a class method I<or> an object
-method. That way you can say:
-
- $me = Person->new();
- $him = $me->new();
-
-To do this, all we have to do is check whether what was passed in
-was a reference or not. If so, we were invoked as an object method,
-and we need to extract the package (class) using the ref() function.
-If not, we just use the string passed in as the package name
-for blessing our referent.
-
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = {};
$self->{NAME} = undef;
$self->{AGE} = undef;
changes to your Person::new() constructor:
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = {};
$Census++;
$self->{NAME} = undef;
to perl version 5.004 we'll have to quote the field name.)
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = {};
$self->{NAME} = undef;
$self->{AGE} = undef;
a full name field this way:
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = {};
$self->{FULLNAME} = Fullname->new();
$self->{AGE} = undef;
use strict;
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = {
TITLE => undef,
CHRISTIAN => undef,
fix up Employee::new() this way:
sub new {
- my $proto = shift;
- my $class = ref($proto) || $proto;
+ my $class = shift;
my $self = $class->SUPER::new();
$self->{SALARY} = undef;
$self->{ID} = undef;
our $VERSION = '1.1';
-and then in Employee.pm could you can say
+and then in Employee.pm you can say
- use Employee 1.1;
+ use Person 1.1;
And it would make sure that you have at least that version number or
higher available. This is not the same as loading in that exact version
package Person;
sub new {
- my $that = shift;
- my $class = ref($that) || $that;
+ my $class = shift;
my $self = {
NAME => undef,
AGE => undef,
);
sub new {
- my $that = shift;
- my $class = ref($that) || $that;
+ my $class = shift;
my $self = {
_permitted => \%fields,
%fields,
);
sub new {
- my $that = shift;
- my $class = ref($that) || $that;
- my $self = bless $that->SUPER::new(), $class;
+ my $class = shift;
+ my $self = $class->SUPER::new();
my($element);
foreach $element (keys %fields) {
$self->{_permitted}->{$element} = $fields{$element};
struct 'Fred' => {
one => '$',
many => '@',
- profession => Jobbie, # calls Jobbie->new()
+ profession => 'Jobbie', # does not call Jobbie->new()
};
- $ob = Fred->new;
+ $ob = Fred->new(profession => Jobbie->new());
$ob->one("hmmmm");
$ob->many(0, "here");
user-defined types (classes). User types will be initialized by calling
that class's new() method.
+Take care that the C<Jobbie> object is not created automatically by the
+C<Fred> class's new() method, so you should specify a C<Jobbie> object
+when you create an instance of C<Fred>.
+
Here's a real-world example of using struct generation. Let's say you
wanted to override Perl's idea of gethostbyname() and gethostbyaddr() so
that they would return objects that acted like C structures. We don't
# this is the same as before...
sub new {
- my $that = shift;
- my $class = ref($that) || $that;
+ my $class = shift;
my $self = {
NAME => undef,
AGE => undef,