Beefy Boxes and Bandwidth Generously Provided by pair Networks
"be consistent"

comment on

( [id://3333]=superdoc: print w/replies, xml ) Need Help??
perlfunc's entry on substr says:

If the lvalue returned by substr is used after the EXPR is changed in any way, the behaviour may not be as expected and is subject to change. This caveat includes code such as print(substr($foo,$a,$b)=$bar) or (substr($foo,$a,$b)=$bar)=$fud (where $foo is changed via the substring assignment, and then the substr is used again), or where a substr() is aliased via a foreach loop or passed as a parameter or a reference to it is taken and then the alias, parameter, or deref'd reference either is used after the original EXPR has been changed or is assigned to and then used a second time.

I had to read that last sentence several times to understand it, but I think it covers what your code does: you've taken a reference to a substr, changed the referee string, taken a reference to a substring of that referee, and changed the referee of that. Don't do that.

Here's some code that does what you want:

#!/usr/bin/perl -l use warnings; use strict; sub recurse($); sub recurse($) { my $a = $_[0]; print ">> '$a'"; $a =~ s/ ^ (.) (.+) (.) $ / join '', $1, recurse $2, $3 /ex; print "<< '$a'"; " ( $a ) "; } print "Result: ", recurse 'aaaaaaaaaa';


Update: diotalevi pointed out that my description of the problem with the OP's code was wrong. I've fixed it.

In reply to Re: Scalar refs, aliasing, and recursion weirdness. by MarkusLaker
in thread Scalar refs, aliasing, and recursion weirdness. by BrowserUk

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

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?

What's my password?
Create A New User
Domain Nodelet?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others chilling in the Monastery: (6)
As of 2024-05-30 09:41 GMT
Find Nodes?
    Voting Booth?

    No recent polls found