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

1. #!/usr/bin/perl -w
2. package person;
3. use strict;
4. sub sleep() {
5. my ($self) = @_;
6. my $name = $self->{"name"};
7. print("$name is person, he is sleeping\n");
8. }
9. sub study() {
10. my ($self) = @_;
11. my $name = $self->{"name"};
12. print("$name is person, he is studying\n");
13. }
14. return 1;

dog.pm

1. #!/usr/bin/perl -w
2. package dog;
3. use strict;
4. sub sleep() {
5. my ($self) = @_;
6. my $name = $self->{"name"};
7. print("$name is dog, he is sleeping\n");
8. }
9. sub bark() {
10. my ($self) = @_;
11. my $name = $self->{"name"};
12. print("$name is dog, he is barking\n");
13. }
14. return 1;

bless.pl

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

bless.wrong.pl

1. #!/usr/bin/perl =w
2. use strict;
3. use person;
4. use dog;
5. sub main()
6. {
7. my $object = {"name" => "tom"};
8. # 没有把类型信息和$object绑定，因此无法获知$object有sleep方法
9. $object->sleep();
10. $object->study();
11. }
12. &main();
13. # 程序运行输出为：
14. # 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

1. #include <stdio.h>
2. #include <stdlib.h>
3. #include <string.h>
4. struct object {
5. char name[16];
6. };
7. struct person {
8. char name[16];
9. void sleep() { printf("%s is person, he is sleeping\n", this->name); }
10. void study() { printf("%s is person, he is studying\n", this->name); }
11. };
12. struct dog {
13. char name[16];
14. void sleep() { printf("%s is dog, he is sleeping\n", this->name); }
15. void bark() { printf("%s is dog, he is barking\n", this->name); }
16. };
17. #define bless(object, type) ((type*) object)
18. int main()
19. {
20. struct object * o = (struct object *) malloc(sizeof(struct object));
21. strcpy(o->name, "tom");
22. // 先把"tom"变为人
23. bless(o, person)->sleep();
24. bless(o, person)->study();
25. // 再把"tom"变为狗
26. bless(o, dog)->sleep();
27. bless(o, dog)->bark();
28. // 最后，再把"tom"变回人
29. bless(o, person)->sleep();
30. bless(o, person)->study();
31. return 0;
32. }
33. // 程序运行时输出：
34. // tom is person, he is sleeping
35. // tom is person, he is studying
36. // tom is dog, he is sleeping
37. // tom is dog, he is barking
38. // tom is person, he is sleeping
39. // tom is person, he is studying

关键的地方就是把对象o的类型转变为person类型和dog类型