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blessbless.wrong.pl ： 错误的使用blessbless.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 -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 CODE:#!/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 CODE:#!/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# tom is person, he is studying

bless.wrong.pl CODE:#!/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：# 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 #include #include

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

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