【Perl学习笔记】2. perl中的bless理解

waiwai64

　　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
bless.cc ： 使用C++语言实现了与bless.pl相同功能的代码
　　
person.pm
CODE:
#!/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
CODE:
#!/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
CODE:
#!/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
CODE:
#!/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.
　　
使用c++实现bless的功能
　　c中的代码
CODE:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
　　struct object {
       char name[16];
};
　　struct person {
       char name[16];
　　void sleep() { printf("%s is person, he is sleeping/n", this->name); }
       void study() { printf("%s is person, he is studying/n", this->name); }
};
　　struct dog {
       char name[16];
　　void sleep() { printf("%s is dog, he is sleeping/n", this->name); }
       void bark() { printf("%s is dog, he is barking/n", this->name); }
};
　　#define bless(object, type) ((type*) object)
　　int main()
{
       struct object * o = (struct object *) malloc(sizeof(struct object));
       strcpy(o->name, "tom");
　　// 先把"tom"变为人
       bless(o, person)->sleep();
       bless(o, person)->study();
　　// 再把"tom"变为狗
       bless(o, dog)->sleep();
       bless(o, dog)->bark();
　　// 最后，再把"tom"变回人
       bless(o, person)->sleep();
       bless(o, person)->study();
       return 0;
}
　　// 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