perl assignment to hash in subroutine return gets weird

Question

Running perl 5.12.4 Am getting disparity between result of a function when a hash is assigned within the return statement or beforehand. Easiest example is:

perl -e 'sub s1 {
  my @a=qw/b 1 c 2 a 3 a 4/;
  my %h=@a;
  return %h
  }
  print "@{[ s1()]}\n"'
c 2 a 4 b 1


perl -e 'sub s1 {
  my @a=qw/b 1 c 2 a 3 a 4/;
  my %h=@a;
  return %h=@a
  }
  print "@{[ s1()]}\n"'
c 2 c 2 a c

Why does (re)assigning to hash in return statement (2nd example) corrupt the returned hash?

Confirmed. This is truly weird. But when I ran the code on v14.2 or v16.3 it ran without issue → it seems to have been fixed, although I can't see any mention of related fixes in the perldeltas. — amon
– amon, Commented May 7, 2013 at 5:24
Running your second example on perl 5.16.2, I get b 1 c 2 a 4 — friedo
– friedo, Commented May 7, 2013 at 5:26
This is a bit odd. I can replicate this on one of my machines: This is perl 5, version 12, subversion 4 (v5.12.4) built for darwin-thread-multi-2level — chrsblck
– chrsblck, Commented May 7, 2013 at 6:24
the return of hash/hash element assignments in list context have always been a little wonky — ysth
– ysth, Commented May 7, 2013 at 10:48

ikegami · Accepted Answer · 2013-05-07 10:40:03Z

2

Because of a bug. It appears to have been fixed in 5.14.0. (Present in 5.12.4. Not present in 5.14.0)

Minimal test case:

perl -E"say %h = qw/b 1 c 2 a 3 a 4/"

edited May 7, 2013 at 10:40

answered May 7, 2013 at 10:33

ikegami

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2 Comments

Rob N Over a year ago

Thank you all for your responses. I accept that my site needs to update its Perl version to 5.14. It is always nice to have one's sanity confirmed when the software foundations start to give way.

Brad Gilbert Over a year ago

@RobN You mean update to at-least 5.14 (5.18 should be available in a week or-so. Although it may cause subtle bugs in your codebase to show their faces en-mass.)

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