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Factory Method
this example from a Well House Consultants training course
Source code: B7.pl Module: P310
{
use strict; package Banana; use Time::Local; sub new { my ($class,$d,$m,$y,$paid,$q) = @_; my %info; $info{"date"} = timegm(0,0,12,$d,$m-1,$y); $info{"paid"} = $paid; $info{"quantity"} = $q; bless \%info,$class; } sub getpriceeach { my ($which) = @_; $which->{"paid"} / $which->{"quantity"}; } sub getwhen{ my ($which) = @_; my $lt = localtime($which->{"date"}); $lt =~ s/\d+:\d+:\d+\s//; # Strip out time return $lt; } # 00183 14/2/2011 1.72 1.35 sub orderline { # Factory method my ($class,$string) = @_; my ($stockitem, $date, $price, $q) = split(/\s+/,$string); my ($d,$m,$y) = split(/\//,$date); my $built; if ($stockitem eq "00183") { $built = Banana::new("BestBanana",$d,$m,$y,$price,$q); } elsif ($stockitem eq "00176") { $built = Banana::new("LargeBanana",$d,$m,$y,$price,$q); } else { $built = Banana::new("SmallBanana",$d,$m,$y,$price,$q); } return $built; } } { use strict; package LargeBanana;; # sold "each" ... inherit "getpriceeach" from Banana our @ISA = qw(Banana); } { use strict; package BestBanana; our @ISA = qw(Banana); sub getpriceeach { # sold per kg; 7 bananas in a kg my ($which) = @_; # override "getpriceeach" $which->{"paid"} / $which->{"quantity"} / 7 ; } } { use strict; package SmallBanana; our @ISA = qw(Banana); sub getpriceeach { # these come wrapped in 10s !! my ($which) = @_; # override "getpriceeach" $which->{"paid"} / $which->{"quantity"} / 10 ; } } $sept = new SmallBanana (7,9,2010,1.60,1); $oct = new BestBanana (14,10,2010,1.75,1.4); $nov = new LargeBanana (5,11,2010,1.80,8); $dec = "Minced Pie and Custard"; $jan = new BestBanana (6,1,2011,1.65,1.35); $feb = orderline Banana("00176 14/2/2011 1.78 8"); $mar = orderline Banana("00183 12/3/2011 1.72 1.35"); @breakfast = ($sept, $oct, $nov, $dec, $jan, $feb, $mar); foreach $item(@breakfast) { # isa method in universal superclass lets you work out if an object # is something or inherits from it. if ($item->isa("Banana")) { $pr = $item->getpriceeach(); print "price of this item (each) is $pr\n"; } else { print "Cannot work out price each\n"; } # can will tell you if an object supports a method if ($item->can("getwhen")) { $pr = $item->getwhen(); print "Purchased $pr\n"; } else { print "Unknown purchase date\n"; } # IMPORTANT WARNING ... if you find yourself using these a lot you # probably have GOT THE DESIGN WRONG! You should be using polymorphism # to do this lot! } __END__ munchkin:pl grahamellis$ perl B7.pl price of this item (each) is 0.16 Purchased Tue Sep 7 2010 price of this item (each) is 0.178571428571429 Purchased Thu Oct 14 2010 price of this item (each) is 0.225 Purchased Fri Nov 5 2010 Cannot work out price each Unknown purchase date price of this item (each) is 0.174603174603175 Purchased Thu Jan 6 2011 price of this item (each) is 0.2225 Purchased Mon Feb 14 2011 price of this item (each) is 0.182010582010582 Purchased Sat Mar 12 2011 munchkin:pl grahamellis$ Learn about this subject
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