在Perl中导出vs export_ok [英] export vs export_ok in perl

问题描述

我不明白EXPORT_OK与EXPORT的区别/用例是什么.
大多数资源在以下几行中都提到了一些东西:

I can not understand what is the difference/use case of EXPORT_OK vs EXPORT.
Most resources mentions something in the lines of:

@Export允许将模块的功能和变量导出到 用户使用标准导入方法的名称空间.这样一来，我们就不会 需要为模块创建对象以访问其成员.
@EXPORT_OK会根据需求导出符号以选择列表 模块的符号(子例程和变量)的集合.

@Export allows to export the functions and variables of modules to user’s namespace using the standard import method. This way, we don’t need to create the objects for the modules to access its members.
@EXPORT_OK does export of symbols on demand basis for selective list of symbols (subroutines and variables) of the module.

但是我真的看不到这里的区别/含义.
有人可以提供这两个符号的区别/用途的基本例子吗?

But I really don't see the difference/meaning here.
Can someone please provide a small fundamental example of the difference/usage of these 2 symbols?

推荐答案

假设我有一个使用@EXPORT的软件包MyPackage.

Let's say I have a package MyPackage that uses @EXPORT.

#this is MyPackage.pm
package MyPackage;
@EXPORT = qw(do_awesome_thing);

sub do_awesome_thing { ... }

sub be_awesome { ... }

现在，当我在代码中使用MyPackage时，

Now, when I use MyPackage in my code,

#this is myscript.pl
use MyPackage;

do_awesome_thing(); #works

be_awesome(); #doesn't work
MyPackage::be_awesome(); #works

do_awesome_thing会自动从MyPackage导出到我的代码，而无需我说把这个给我". be_awesome不会被导出(也不会与@EXPORT_OK一起导出，我只是在演示该部分以使您清楚导出"给了我们什么).

do_awesome_thing gets automatically exported to my code from MyPackage, without me having to say "give this to me". be_awesome isn't exported (and it won't be exported with @EXPORT_OK either, I'm just showing that part to get you clear on what "exporting" gives us).

另一方面，如果我有使用@EXPORT_OK的软件包MyOtherPackage，

On the other hand, if I have a package MyOtherPackage that uses @EXPORT_OK,

#this is MyOtherPackage.pm
package MyOtherPackage;
@EXPORT_OK = qw(do_awesome_thing);

sub do_awesome_thing { ... }

sub be_awesome { ... }

然后尝试

#this is mynewscript.pl
use MyOtherPackage;

do_awesome_thing(); #doesn't work
MyOtherPackage::do_awesome_thing(); #works, as always

直接调用do_awesome_thing的行将不起作用.这是因为在@EXPORT_OK中放入内容表示仅在用户要求时将其提供给我的用户".由于我们只是说use MyOtherPackage而没有在这里明确要求导入do_awesome_thing，因此它不会被导入，并且只能通过指定程序包名称来访问.

the line calling do_awesome_thing directly won't work. This is because putting something in @EXPORT_OK says "give this to my users only if they ask for it". Since we've just said use MyOtherPackage without explicitly asking for do_awesome_thing to be imported here, it doesn't get imported, and is accessible only by specifying the package name.

您要求导入do_awesome_thing的方式是在上面mynewscript.pl的第二行中说use MyOtherPackage qw(do_awesome_thing).这就是说导入该模块并使do_awesome_thing直接可用.之后，上面mynewscript.pl中的第四行将开始工作.

The way you ask for do_awesome_thing to be imported is to say use MyOtherPackage qw(do_awesome_thing) in the second line of mynewscript.pl above. This says import that module and make do_awesome_thing available directly. After that, the fourth line in mynewscript.pl above will start working.

请注意，用户也可以在第一个程序包中指定use MyPackage qw(do_awesome_thing)，在这种情况下，不会导出@EXPORT列表中的任何其他内容，而只会导出do_awesome_thing.因此，除了use PackageName;的默认情况之外，@EXPORT和@EXPORT_OK的行为类似.在默认情况下，@EXPORT中的任何内容都会自动引发到用户的脚本中，而@EXPORT_OK则更为礼貌并且不会导出任何内容.

Note that the user can specify use MyPackage qw(do_awesome_thing) with the first package also, and in that case, anything else in the @EXPORT list won't be exported, only do_awesome_thing will be. So, except for the default case of use PackageName;, @EXPORT and @EXPORT_OK behave similarly. In the default case, anything in @EXPORT gets thrown into the user's script automatically, while @EXPORT_OK is more polite and doesn't export anything.

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