Further to RMGir here:

If you want to pass a local copy, specify that:

pass1({ params => {%$hashref} });  # {%$hashref} makes a copy of the hash '$hashref'
                                   # points to and creates a new ref to it.

... and stevieb here:

You need to "copy" the reference in order to break the link:

my $params = { %{ $self->{params} } };

There's a pitfall here. Be aware that the "copy" above is only a shallow copy. Any references nested within the referent of the reference being shallow-copied still allow complete read/write access to their referents. 

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $hashref = { foo => { bar => 'nice' } };
 dd 'before pass1: ', $hashref;
 ;;
 pass1({ params => { %$hashref } });
 ;;
 dd 'after pass1: ', $hashref;
 ;;
 ;;
 sub pass1 {
   my $self = shift;
   my $params = $self->{params};
   dd 'in pass1, before assignments ', $params;
   ;;
   $params->{fizz} = 'fazz';
   $params->{foo}{bar} = 'KaPow';
   dd 'in pass1 after assignments ', $params;
   }
"
("before pass1: ", { foo => { bar => "nice" } })

("in pass1, before assignments ", { foo => { bar => "nice" } })

(
  "in pass1 after assignments ",
  { fizz => "fazz", foo => { bar => "KaPow" } },
)

("after pass1: ", { foo => { bar => "KaPow" } })

[download]
Bottom line: references be tricky. (Update: See perlref, perlreftut, maybe also perldsc.)

Give a man a fish:  <%-{-{-{-<

In reply to Re: How to preserve values outside a sub by AnomalousMonk
in thread How to preserve values outside a sub by Anonymous Monk

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.