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
- #!/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[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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关键的地方就是把对象o的类型转变为person类型和dog类型