perl bless

程序说明

网上的很多教程都没有把bless讲清楚，我通过摸索和实验，终于明白bless是什么意思了，简单的讲：


    * bless有两个参数：对象的引用、类的名称。
    * 类的名称是一个字符串，代表了类的类型信息，这是理解bless的关键。
    * 所谓bless就是把 类型信息 赋予 实例变量。


程序包括5个文件：
person.pm ：实现了person类
dog.pm ：实现了dog类
bless.pl ： 正确的使用bless
bless.wrong.pl ： 错误的使用bless


person.pm

#!/usr/bin/perl -w
package person;
use strict;

sub sleep() {
        my ($self) = @_;
        my $name = $self->{"name"};

        print("$name is person, he is sleeping\n");
}

sub study() {
        my ($self) = @_;
        my $name = $self->{"name"};

        print("$name is person, he is studying\n");
}
return 1;

dog.pm

#!/usr/bin/perl -w
package dog;
use strict;

sub sleep() {
        my ($self) = @_;
        my $name = $self->{"name"};

        print("$name is dog, he is sleeping\n");
}

sub bark() {
        my ($self) = @_;
        my $name = $self->{"name"};

        print("$name is dog, he is barking\n");
}

return 1;

bless.pl

#!/usr/bin/perl =w
use strict;
use person;
use dog;

sub main()
{
        my $object = {"name" => "tom"};

        # 先把"tom"变为人
        bless($object, "person");
        $object->sleep();
        $object->study();

        # 再把"tom"变为狗
        bless($object, "dog");
        $object->sleep();
        $object->bark();

        # 最后，再把"tom"变回人
        bless($object, "person");
        $object->sleep();
        $object->study();
}

&main();

# 程序运行时输出：
# tom is person, he is sleeping
# tom is person, he is studying
# tom is dog, he is sleeping
# tom is dog, he is barking
# tom is person, he is sleeping
# tom is person, he is studying

bless.wrong.pl

#!/usr/bin/perl =w
use strict;
use person;
use dog;

sub main()
{
        my $object = {"name" => "tom"};

        # 没有把类型信息和$object绑定，因此无法获知$object有sleep方法
        $object->sleep();
        $object->study();
}

&main();

# 程序运行输出为：
# Can't call method "sleep" on unblessed reference at bless.wrong.pl line 10.