[Perl]继承SUPER,-norequire,use parent

2016-10-13 12:39:16来源:CSDN作者:BruceXiaoYY人点击

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parent

package Baz;use parent qw(Foo Bar);

is equivalent to:

package Baz;BEGIN {  require Foo;  require Bar;  push @ISA, qw(Foo Bar);}

-norequire

package Foo;sub exclaim { "I CAN HAS PERL" }package DoesNotLoadFooBar;use parent -norequire, 'Foo', 'Bar';# will not go looking for Foo.pm or Bar.pm

 is equivalent to 

package Foo;sub exclaim { "I CAN HAS PERL" }package DoesNotLoadFooBar;push @DoesNotLoadFooBar::ISA, 'Foo', 'Bar';

This is also helpful for the case where a package lives within a differently named file:

package MyHash;use Tie::Hash;use parent -norequire, 'Tie::StdHash';#This is equivalent to the following code:package MyHash;require Tie::Hash;push @ISA, 'Tie::StdHash';

If you want to load a subclass from a file that require would not consider an eligible filename (that is, it does not end in either .pm or .pmc), use the following code:

package MySecondPlugin;require './plugins/custom.plugin'; # contains Plugin::Customuse parent -norequire, 'Plugin::Custom';

SUPER

By default, every base class needs to live in a file of its own. If you want to have a subclass and its parent class in the same file, you can tell parent not to load any modules by using the -norequire switch:

package A;sub new {  return bless {}, shift;}sub speak {  my $self = shift;  say 'A';}package B;use parent -norequire, 'A';sub speak {  my $self = shift;  $self->SUPER::speak();  say 'B';}package C;use parent -norequire, 'B';sub speak {  my $self = shift;  $self->SUPER::speak();  say 'C';}my $c = C->new();$c->speak();#---------In this example, we will get the following output:ABC

This demonstrates how SUPER is resolved. Even though the object is blessed into the C class, the speak() method in the B class can still call SUPER::speak() and expect it to correctly look in the parent class of B (i.e the class the method call is in), not in the parent class of C (i.e. the class the object belongs to).
There are rare cases where this package-based resolution can be a problem. If you copy a subroutine from one package to another, SUPER resolution will be done based on the original package.

Summay

  1.  A subclass and its parent class can be in the same file.
  2. use parent -norequire, qw (parent) avoid compiling, which causes syntax error in scenario 1.
  3. SUPER:: calls parent ‘s method of current object
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