12.5.2 访问被覆盖的方法

12.5.2  访问被覆盖的方法

当一个类定义一个方法,那么该子过程覆盖任意基类中同名的方法。

想象一下你有一个Mule(骡)对象(它是从Horse(马)类和Donkey（驴）类衍生而来的)

$stallion = Horse->new(gender => "male"); 男性

$molly = Mule->new(gender => "female"); 女性

$colt = $molly->breed($stallion);



这就是SUPER 伪类提供便利的地方,它令你能够调用一个覆盖了的基类方法,而不用声明哪个类定义了该方法。




[root@node01 aaa]# cat Horse.pm 
package Horse;    
our @ISA = "Critter";    
require 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;    
#return  $self;    
};    
sub sum1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b + 7;    
};   
  
sub kick {  
  my $self=shift;  
  $self->SUPER::kick(@_);  
};  
1; 


Horse 类继承了Critter 类

[root@node01 aaa]# 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 sum2 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b;    
};    
    
    
sub fun1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a / $b;    
}    
  
sub kick {  
      my  $self=shift;  
       my $a=shift;  
       my $b=shift;  
       return $a / $b +66;  
}  
  
1;  



[root@node01 aaa]# cat a1.pl 
use Horse;  
use Data::Dumper;  
  
$steed = Horse->new(color => "dun");  
print $steed->kick(12,4);  
print "
";  
[root@node01 aaa]# perl a1.pl 
69

此时调用了Critter.pm  类的kick  方法:



[root@node01 aaa]# cat Critter.pm 
package Critter;    
our @ISA = "Mule";    
require Mule;  
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 sum2 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b;    
};    
    
    
sub fun1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a / $b;    
}    
  
sub kick {  
      my  $self=shift;  
       my $a=shift;  
       my $b=shift;  
       return $a / $b +66;  
}  
  
1;   


让 Critter 继承Mule 类

[root@node01 aaa]# cat Mule.pm 
package Mule;
sub kick {  
      my  $self=shift;  
       my $a=shift;  
       my $b=shift;  
       return $a * $b +66;  
}  
  
1;

[root@node01 aaa]# perl a1.pl 
69




修改
[root@node01 aaa]# cat Critter.pm 
package Critter;    
our @ISA = "Mule";    
require Mule;  
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 sum2 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b;    
};    
    
    
sub fun1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a / $b;    
}    
  
 sub kick {  
  my $self=shift;  
  $self->SUPER::kick(@_);  
};  
1;


[root@node01 aaa]# cat a1.pl 
use Horse;  
use Data::Dumper;  
  
$steed = Horse->new(color => "dun");  
print $steed->kick(12,4);  
print "
";  
[root@node01 aaa]# perl a1.pl 
114




当一个类定义一个方法，那么该子过程覆盖任意基类中同名的方法:

[root@node01 111]# cat Horse.pm 
package Horse;    
our @ISA = "Critter";    
require 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;    
#return  $self;    
};    
sub sum1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b + 7;    
};   
  
sub kick {  
  my $self=shift;  
  my $a=shift;
  my $b=shift;
  return $a * $b;
};  
1;  

[root@node01 111]# cat Critter.pm 
package Critter;    
our @ISA = "Mule";    
require Mule;  
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 sum2 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a + $b;    
};    
    
    
sub fun1 {    
       $self=shift;    
       my $a=shift;    
       my $b=shift;    
       return $a / $b;    
}    
  
 sub kick {  
  my $self=shift;  
  my $a=shift;
  my $b=shift;
  return $a/$b +5;
};  
1;    

[root@node01 111]# cat a1.pl 
use Horse;  
use Data::Dumper;  
  
$steed = Horse->new(color => "dun");  
print $steed->kick(12,4);  
print "
";  
[root@node01 111]# perl a1.pl 
48

此时没有去访问基类的方法:


Mule （骡）
类的设计者通过给 Mule（骡）类写自己的 breed 方法覆盖了那些父类的 breed 方法。
这这意味着下面的交叉引用可能不能正确工作：

$stallion = Horse->new(gender => "male"); 男性

$molly = Mule->new(gender => "female");    女性

$colt = $molly->breed($stallion);