Howdy monks. I have this application that uses YAML::XS which has worked wonderfully well... until I hit this problem: 

   my @arr;
   push @arr, { xx=>\99 } for 1..2;
   my $arr2 = YAML::XS::Load( YAML::XS::Dump( \@arr ) );
   $arr2->[0]->{xx}='THIS VALUE IS MEANT TO CHANGE ONE ROW ONLY';
   say "NO WAY!" if $arr2->[0]->{xx} eq $arr2->[1]->{xx}; # which prin
+ts NO WAY!

[download]

I don't get it. In the for loop, doesn't \99 resolve to 2 different references to 2 different values (which is 99)? So why after dumping/loading, writing to row 0 also modifies the HASH in row 1?

Actually, if you view the YAML text generated by Dump(): 

---
- xx: &1 !!perl/ref
    =: 99
- xx: *1

[download]

This tells you there's an alias (*1 ==> &1) that makes both xx attributes point to the same place. The problem is that Load() seemingly treats the xx key as the same memory location, which is not remotely a decent interpretation of the serialized data-- "hold a reference to the same data" does not mean "we're in the same address".

I wish I could switch to JSON or another YAML module (YAML::Syck, YAML etc do not have the same behavior), but right now some serious production code depends on this YAML::XS (and the speed is nice too) hence no changes can be undertaken in the near future.

So I dove into the YAML::XS C code, but could not find the culprit:

https://github.com/ingydotnet/yaml-libyaml-pm/blob/master/LibYAML/perl_libyaml.c

Rod

In reply to YAML scalar ref strange behavior by rodd

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.