Perl Symbolic Reference

看一些模块的代码，很多时候通过*glob的方式来改变变量或者函数，这种方法称为Symbolic reference。

首先看一下*glob的结构，这个在之前的博文已经讲过，不做细述：

SV = PVGV(0x18d1364) at 0x182aaec
  REFCNT = 2
  FLAGS = (IN_PAD)
  NAME = "test"
  NAMELEN = 4
  GvSTASH = 0x298fc4	"main"
  GP = 0x18b90ac
    SV = 0x0
    REFCNT = 1
    IO = 0x0
    FORM = 0x0  
    AV = 0x0
    HV = 0x0
    CV = 0x0
    CVGEN = 0x0
    LINE = 4
    FILE = "test.pl"
    FLAGS = 0x8
    EGV = 0x182aaec	"test"

运行下边的代码段，察看一下输出对应的ref slot。

print ref \1;
print ref \'testing';
print ref [qw(one, two ,three)];
print ref {};
print ref sub {};

如何给*glob赋值？通过下面的方式，填充Symbol的不同slot，从而使得对应的$test,@test,%test,&test非空。

use Data::Dumper;
use Devel::Peek;

*test = \1;
*test = [qw(one two three)];
*test = {qw(one two three four)};
*test = sub {};

print Dump *test;

$scalar = 1;
*test   = \$scalar;
@array  = 1..4;
*test   = \@array;
%hash   = 1..4;
*test   = \%hash;

print Dump *test;

SV = PVGV(0x18d134c) at 0x182aaec
  REFCNT = 6
  FLAGS = (MULTI,ASSUMECV,IN_PAD)
  NAME = "test"
  NAMELEN = 4
  GvSTASH = 0x298fc4	"main"
  GP = 0x18b9104
    SV = 0x182aadc
    REFCNT = 1
    IO = 0x0
    FORM = 0x0  
    AV = 0x2990d4
    HV = 0x299214
    CV = 0x18b1e7c
    CVGEN = 0x0
    LINE = 4
    FILE = "test.pl"
    FLAGS = 0xe
    EGV = 0x182aaec	"test"

如何使用？use strict情况下有几种方式：
下面的情况直接调用Symbol或者通过our定义直接访问变量，函数无需our定义，总是一个Symbol，可以直接通过名字访问。

use strict;
use Data::Dumper;
use Devel::Peek;

*test = \1;
*test = [qw(one two three)];
*test = {qw(one two three four)};
*test = sub {print "testing\n";};

print $::test;
print %::test;
&test();

our ($test, %test);
print $test;
print %test;
&test;

如果通过一个变量传名字访问另外一个变量，则需要通过下面的方式no strict 'refs'。

no strict 'refs';
print ${'test'};
print %{'test'};
&{'test'};

参考：

perldoc perlref