草莓Perl是%ENV一个普通的对象

Question

因此,在Strawberry Perl中,%ENV似乎是一个普通的哈希(至少它没有绑定),但它似乎也解决了密钥不敏感的问题.这是有道理的,因为环境变量在PowerShell中不区分大小写(我不确定Windows环境变量和大小写之间的确切关系).所以,我想知道%ENV如何同时是一个普通的哈希,并且当你调用它们内置的密钥时,它们没有列出的"隐式"密钥.%ENV哈希是否神奇而不被束缚？

use strict;
use warnings;

# Env appears to be an ordinary hash
# 'TEMP' is present in the list of environment variables
# but 'temp' is not
printf "$_\n" foreach keys %ENV;

print "\n";

# this gives us the value of $ENV:TEMP
# which makes sense.
printf "uppercase 'temp' maps to %s\n", $ENV{TEMP};

# even though temp is not present in the
# list of keys, the same value appears as for
# $ENV{TEMP}
# This seems to make sense given the behavior of powershell
# (I am not quite sure what the relationship is between
# Windows environment variables and case, but this seems reasonable.)
printf "lowercase 'temp' maps to %s\n", $ENV{temp};

# However, %ENV is not a tied hash.
printf "Tie status: %s\n", tied(%ENV) // "not a tied variable";

Answer 1

以下是来自ActivePerl,但包括Strawberry Perl在内的每个Perl都会给你同样的东西:

>perl -E"use Devel::Peek; Dump(\%ENV, 1);"
SV = IV(0x74b154) at 0x74b154
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x63e33c
  SV = PVHV(0x62a8ac) at 0x63e33c
    REFCNT = 2
    FLAGS = (SMG,RMG,SHAREKEYS)
    MAGIC = 0x639084                               <-------
      MG_VIRTUAL = &PL_vtbl_env
      MG_TYPE = PERL_MAGIC_env(E)
    ARRAY = 0x640794  (0:30, 1:22, 2:11, 3:1)
    hash quality = 107.7%
    KEYS = 47
    FILL = 34
    MAX = 63

如你所见,%ENV是神奇的.但它并没有束缚; 这将是魔术类型"P"而不是"E".