perl bless 的理解

从网上找了一篇不错的讲解 perl 里面的 bless 功能的文章

注： 以下文章摘自： http://www.cnblogs.com/Cmpl/archive/2011/08/17/2142841.html

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

1. #!/usr/bin/perl -w
2. package person;
3. use strict;
5. sub sleep() {
6.         my ($self) = @_;
7.         my $name = $self->{"name"};
9.         print("$name is person, he is sleeping\n");
10. }
12. sub study() {
13.         my ($self) = @_;
14.         my $name = $self->{"name"};
16.         print("$name is person, he is studying\n");
17. }
18. return 1;

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dog.pm

1. #!/usr/bin/perl -w
2. package dog;
3. use strict;
5. sub sleep() {
6.         my ($self) = @_;
7.         my $name = $self->{"name"};
9.         print("$name is dog, he is sleeping\n");
10. }
12. sub bark() {
13.         my ($self) = @_;
14.         my $name = $self->{"name"};
16.         print("$name is dog, he is barking\n");
17. }
19. return 1;

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bless.pl

1. #!/usr/bin/perl =w
2. use strict;
3. use person;
4. use dog;
6. sub main()
7. {
8.         my $object = {"name" => "tom"};
10.         # 先把"tom"变为人
11.         bless($object, "person");
12.         $object->sleep();
13.         $object->study();
15.         # 再把"tom"变为狗
16.         bless($object, "dog");
17.         $object->sleep();
18.         $object->bark();
20.         # 最后，再把"tom"变回人
21.         bless($object, "person");
22.         $object->sleep();
23.         $object->study();
24. }
26. &main();
28. # 程序运行时输出：
29. # tom is person, he is sleeping
30. # tom is person, he is studying
31. # tom is dog, he is sleeping
32. # tom is dog, he is barking
33. # tom is person, he is sleeping
34. # tom is person, he is studying

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bless.wrong.pl

1. #!/usr/bin/perl =w
2. use strict;
3. use person;
4. use dog;
6. sub main()
7. {
8.         my $object = {"name" => "tom"};
10.         # 没有把类型信息和$object绑定，因此无法获知$object有sleep方法
11.         $object->sleep();
12.         $object->study();
13. }
15. &main();
17. # 程序运行输出为：
18. # 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

1. #include <stdio.h>
2. #include <stdlib.h>
3. #include <string.h>
5. struct object {
6.         char name[16];
7. };
9. struct person {
10.         char name[16];
12.         void sleep() { printf("%s is person, he is sleeping\n", this->name); }
13.         void study() { printf("%s is person, he is studying\n", this->name); }
14. };
16. struct dog {
17.         char name[16];
19.         void sleep() { printf("%s is dog, he is sleeping\n", this->name); }
20.         void bark() { printf("%s is dog, he is barking\n", this->name); }
21. };
23. #define bless(object, type) ((type*) object)
25. int main()
26. {
27.         struct object * o = (struct object *) malloc(sizeof(struct object));
28.         strcpy(o->name, "tom");
30.         // 先把"tom"变为人
31.         bless(o, person)->sleep();
32.         bless(o, person)->study();
34.         // 再把"tom"变为狗
35.         bless(o, dog)->sleep();
36.         bless(o, dog)->bark();
38.         // 最后，再把"tom"变回人
39.         bless(o, person)->sleep();
40.         bless(o, person)->study();
41.         return 0;
42. }
44. // 程序运行时输出：
45. // tom is person, he is sleeping
46. // tom is person, he is studying
47. // tom is dog, he is sleeping
48. // tom is dog, he is barking
49. // tom is person, he is sleeping
50. // 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