第十二章 对象(下)

第十二章 对象(下)12.5.1 通过 @ISA 继承package Mule;our @ISA= ("Horse", "Donkey");Perl 将首先在Horse 里(和他的任何前辈类里,比如Critter)查找任何在Mule里找不到的方法,找不到以后才继续在Donkey 和其父类里进行查找。如果缺失的方法在一个基类里发现,Perl内部把该位置缓存到当前类里,依次提高效率,当 Perl 搜索一个方法的时候，它确信你没有创建一个闭环的继承级别。如果两个类互相 继承则可能出现这个问题Vsftp:/root/perl/9# perl a1.pl Recursive inheritance detected in package 'Horse' at Critter.pm line 2.Compilation failed in require at a1.pl line 3.BEGIN failed--compilation aborted at a1.pl line 3.使用use base 声明父类:Vsftp:/root/perl/9# cat Horse.pm package Horse;use base ("Critter");sub new {my $invocant = shift;my $class = ref($invocant) || $invocant;my $self = {color => "bay",legs => 4,owner => undef,@_, # 覆盖以前的属性};return bless $self, $class;};sub sum_arr {       $self=shift;       my $a=shift;       my $b=shift;       return $a + $b + 7;};1;Vsftp:/root/perl/9# cat Critter.pm package Critter;sub new {    my $self = {};    my $invocant = shift;    my $class = ref($invocant) || $invocant;my ($name)=@_;          my $self = {             "name" =>$name                     };      bless $self, $class; # Use class name to bless() reference    return $self;};sub sum {       $self=shift;       my $a=shift;       my $b=shift;       return $a + $b;};1;Vsftp:/root/perl/9# cat a1.pl unshift(@INC,"/root/perl/9"); use Horse;;use Critter;use Data::Dumper;$ed = Horse->new; # 四腿湾马print $ed->sum_arr(4,5);print "\n";print $ed->sum(4,5);print "\n";Vsftp:/root/perl/9# perl a1.pl 16912.5.2  访问被覆盖的方法:基类就是父类:Vsftp:/root/perl/9# cat Horse.pm package Horse;use base ("Critter");sub new {my $invocant = shift;my $class = ref($invocant) || $invocant;my $self = {color => "bay",legs => 4,owner => undef,@_, # 覆盖以前的属性};return bless $self, $class;};sub sum {       $self=shift;       my $a=shift;       my $b=shift;       return $a + $b + 7;};1;Vsftp:/root/perl/9# cat Critter.pm package Critter;sub new {    my $self = {};    my $invocant = shift;    my $class = ref($invocant) || $invocant;my ($name)=@_;          my $self = {             "name" =>$name                     };      bless $self, $class; # Use class name to bless() reference    return $self;};sub sum {       $self=shift;       my $a=shift;       my $b=shift;       return $a + $b;};1;Vsftp:/root/perl/9# cat a1.pl unshift(@INC,"/root/perl/9"); use Horse;;use Critter;use Data::Dumper;$ed = Horse->new; # 四腿湾马#print $ed->sum_arr(4,5);print "\n";print $ed->sum(4,5);print "\n";Vsftp:/root/perl/9# perl a1.pl 16此时Horse 类覆盖了基类Critter的 sum方法Vsftp:/root/perl/9# cat a1.pl unshift(@INC,"/root/perl/9"); use Horse;;use Critter;use Data::Dumper;$ed = Horse->new; # 四腿湾马print $ed->Critter::sum(4,5);print "\n";print $ed->sum(4,5);print "\n";Vsftp:/root/perl/9# perl a1.pl 916调用父类Critter::sum sum的方法Vsftp:/root/perl/9# cat a1.pl unshift(@INC,"/root/perl/9"); use Horse;;use Critter;use base qw(Critter);use Data::Dumper;$ed = Horse->new; # 四腿湾马print $ed->SUPER::sum(4,5);print "\n";print $ed->sum(4,5);print "\n";Vsftp:/root/perl/9# perl a1.pl 91612.5.3  UNIVERSAL：最终的祖先类12.5.4 方法自动装载12.5.5 私有方法