in reply to Re^2: Modifying the keys in a hash
in thread Modifying the keys in a hash

That's interesting - I wondered if that could be used to modify the hash key without creating a copy of the whole hash so tried: 
use Data::Dump qw(dump); 

my %hash = (
  key1 => 'Value1',
  key2 => 'Value2',
  key3 => 'Value3',  );

print "old hash is " . dump(\%hash) ."\n";
map { s/2/_two/; } %hash;
print "new hash is " . dump(\%hash) ."\n";

# output is:
# old hash is { key1 => "Value1", key2 => "Value2", key3 => "Value3" }
# new hash is { key1 => "Value1", key2 => "Value_two", key3 => "Value3
+" }

[download]
How come 'Value2' is changed to 'Value_two', but 'key2' is unchanged?

(Note: I wasn't suggesting that this method should be used for modifying a hash key, but was trying to rise to the challenge of suggesting another method other than copy and delete!)

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Re^4: Modifying the keys in a hash
by shmem (Chancellor) on Feb 23, 2007 at 16:58 UTC
    How come 'Value2' is changed to 'Value_two', but 'key2' is unchanged?
    Because the keys aren't dealt out into $_ in the same way as the values. Consider: 
    qwurx [shmem] 15:35 ~ > perl -MDevel::Peek -e '%hash = qw(a 1 b 2 c 3)
+; for(%hash){print STDERR "$_: ";Dump $_; s/b/d/;} print "$_ => $hash
+{$_}\n" for sort keys %hash'
c: SV = PVIV(0x8168b10) at 0x8166b44
  REFCNT = 2
  FLAGS = (POK,FAKE,READONLY,pPOK)
  IV = -289776295
  PV = 0x8187928 "c"
  CUR = 1
  LEN = 0
3: SV = PV(0x8167ae8) at 0x8167894
  REFCNT = 2
  FLAGS = (POK,pPOK)
  PV = 0x818f380 "3"\0
  CUR = 1
  LEN = 4
a: SV = PVIV(0x8168b20) at 0x8166cf4
  REFCNT = 2
  FLAGS = (POK,FAKE,READONLY,pPOK)
  IV = -902917054
  PV = 0x817be80 "a"
  CUR = 1
  LEN = 0
1: SV = PV(0x8167b00) at 0x8166c28
  REFCNT = 2
  FLAGS = (POK,pPOK)
  PV = 0x817ecb0 "1"\0
  CUR = 1
  LEN = 4
b: SV = PVIV(0x8168b50) at 0x818dfd8
  REFCNT = 2
  FLAGS = (POK,FAKE,READONLY,pPOK)
  IV = 14385563
  PV = 0x81876b0 "b"
  CUR = 1
  LEN = 0
2: SV = PV(0x8167ba8) at 0x8166d90
  REFCNT = 2
  FLAGS = (POK,pPOK)
  PV = 0x81866b0 "2"\0
  CUR = 1
  LEN = 4
a => 1
b => 2
c => 3

    [download]

    The flags for a hash key are (POK,FAKE,READONLY,pPOK), for values they are (POK,pPOK). Which means you manipulate the actual content modifying a value, but you're operating on fake variables modifying the keys.

    --shmem 

    _($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}
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