perl中bless的理解

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
bless.cc ： 使用C++语言实现了与bless.pl相同功能的代码person.pm

#!/usr/bin/perl -wpackage 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 -wpackage 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 =wuse 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

bless.wrong.pl

#!/usr/bin/perl =wuse 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：

使用c++实现bless的功能

c中的代码

#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

关键的地方就是把对象o的类型转变为person类型和dog类型 原文地址 http://bbs2.chinaunix.net/viewthread.php?tid=981190