Re^2: Reassigning $_ in loop doesn't stick

This is totally wrong!

It's even documented. Just like @array returns its elements as aliases,

grep returns aliases into the original list

$ perl -MDevel::Peek -e'
    my $x;
    Dump $x;
    Dump $_ for $x;
    Dump grep 1, $x;
    Dump do { $x };
    Dump map $_, $x;
    Dump sub { $x }->();
    Dump eval { $x };
' 2>&1 | grep 'SV ='
SV = NULL(0x0) at 0x814ecdc   # Address of $x
SV = NULL(0x0) at 0x814ecdc   # for  aliases
SV = NULL(0x0) at 0x814ecdc   # grep aliases
SV = NULL(0x0) at 0x814ecdc   # do   aliases
SV = NULL(0x0) at 0x814ed9c   # map  copies
SV = NULL(0x0) at 0x814f7f8   # sub  copies
SV = NULL(0x0) at 0x814ed9c   # eval copies
[download]

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Re^3: Reassigning $_ in loop doesn't stick by Limbic~Region (Chancellor) on Jan 21, 2009 at 21:24 UTC
ikegami, I sent you a /msg to this affect but since I found a conflict in map, I figured I would post for everyone's benefit. What version of perl is this and why doesn't it agree with the documentation (map aliases not copies)? Update: Confirmed with 5.10.0 that map aliases not copies I am guessing I am not understanding what you are saying. `#!/usr/bin/perl use strict; use warnings; my @foo = 'a' .. 'd'; map { $_ = uc($_) } @foo; # look Mom, map in a void context print "@foo\n";` [download] Cheers - L~R	[reply] [d/l]
Re^4: Reassigning $_ in loop doesn't stick by kyle (Abbot) on Jan 21, 2009 at 21:31 UTC
Both grep and map operate on aliases in their block, as you show. What ikegami is showing is that `grep` will return aliases to the elements of the list it worked on while `map` will return copies (even if it hasn't modified them).	[reply] [d/l] [select]
Re^4: Reassigning $_ in loop doesn't stick by ikegami (Patriarch) on Jan 21, 2009 at 21:33 UTC
The post to which you replied discusses whether `map` returns aliases or not. This is not related to whether `map` operates on an alias when executing the code block. What version of perl is this and why doesn't it agree with the documentation The docs (for 5.10.0) specify that `grep` returns aliases, but they are silent on whether `map` returns aliases or not. Confirmed with 5.10.0 that map aliases not copies Your snippet discards the return value of `map` without checking whether it's an alias or not.	[reply] [d/l] [select]
Re^5: Reassigning $_ in loop doesn't stick by Limbic~Region (Chancellor) on Jan 21, 2009 at 23:58 UTC
ikegami, I thought this might be what you meant on my way home from work. I just can't think of a good reason for it. It would be quite interesting if it worked in assignment (`my $alias_to_foo = grep $_, $foo;`) but it doesn't. So what benefit is there that the return value is an alias into the original list? Cheers - L~R	[reply] [d/l]
Re^6: Reassigning $_ in loop doesn't stick by ikegami (Patriarch) on Jan 22, 2009 at 05:19 UTC