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
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 -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;
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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;
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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
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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.
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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;
[*]};
[*]
[*]struct person {
[*] char name;
[*]
[*] 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;
[*]
[*] 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
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关键的地方就是把对象o的类型转变为person类型和dog类型
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