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;
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.
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
// tom is person, he is studying
