bless用法详细

bless用法详细

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 unbles sed 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