如何获得Perl的ref()函数以返回REF,IO和LVALUE? [英] How can I get Perl's ref() function to return REF, IO, and LVALUE?
问题描述
ref()的文档中提到了几种可能的返回值.我了解它们中的大多数,但不理解REF
,IO
和LVALUE
.如何编写Perl代码以使ref
返回这些值?
The documentation for ref() mentions several possible return values. I understand most of them, but not REF
, IO
, and LVALUE
. How would I write Perl code to cause ref
to return those values?
在阅读 typeglob和文件句柄上的文档后,我与此代码相距很近的IO
:
After reading the documentation on typeglobs and file handles, I came close for IO
with this code:
open(INPUT, '<', 'foo.pl');
print ref(*INPUT{IO}), "\n"; # Prints IO::Handle
对于REF
和LVALUE
,我尝试了几种奇怪的构造,但没有成功.
For REF
and LVALUE
I tried several bizarre constructions, but had no success.
推荐答案
下面是生产其中大多数的快捷方法:
Here's a quick and easy way to produce most of them:
use 5.010;
say 'SCALAR: ', ref \undef;
say 'ARRAY: ', ref [1..5];
say 'HASH: ', ref { key => 'value' };
say 'CODE: ', ref sub {};
say 'REF: ', ref \\undef;
say 'GLOB: ', ref \*_;
say 'LVALUE: ', ref \substr "abc", 1, 2;
say 'LVALUE: ', ref \vec 42, 1, 2;
say 'FORMAT: ', ref *STDOUT{FORMAT}; # needs declaration below
say 'IO: ', ref *STDIN{IO}; # actually prints IO::Handle
say 'VSTRING: ', ref \v5.10.0;
say 'Regexp: ', ref qr/./;
format =
.
REF只是对另一个引用的引用. LVALUE是标量的特例,如果对其进行修改,它会具有外部影响.
REF is just a reference to another reference. LVALUE is a special case of a scalar that has an external influence if it is modified.
IO is the base type behind the handles, you can make it appear explicitely using Acme::Damn from CPAN. As noted by Michael Carman in the comments, you really shouldn't be unblessing objects — don't use in real code.
use Acme::Damn;
say 'IO: ', ref damn *STDIN{IO}; # really prints IO
ref
函数的源代码也具有一些代码来显示"BIND"和"UNKNOWN",但是应该没有办法使它们不弄乱内部结构.布莱德(Blead)也有一个有趣的未受祝福的"REGEXP"(不同于上面的"Regexp");如果有人知道如何使ref
产生...
The source for the ref
function also has bits of code to display "BIND" and "UNKNOWN", but there shouldn't be a way to get those without messing with the internals. Blead also has an interesting unblessed "REGEXP" (different from the "Regexp" above); if someone knows how to make ref
yield that...
这篇关于如何获得Perl的ref()函数以返回REF,IO和LVALUE?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!