Beefy Boxes and Bandwidth Generously Provided by pair Networks
P is for Practical

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Hi Monks, "strict refs" declaration confuses me. The declaration doesn't allow symbolic references. The following code tries to call, undef and defined subroutines using symbolic references while "strict refs".
# use strict; use warnings; sub walk {} sub run {} my $walkable = defined &{ 'walk' }; undef &{ 'walk' }; &{ 'run' };
The above output the following:
$ perl Can't use string ("run") as a subroutine ref while "strict refs" in us +e at line 9.
According to perldiag, the above error message means:
Only hard references are allowed by "strict refs". Symbolic references are disallowed. See perlref.

I understand why the script throws an exception, but I'm not sure why defined/undef &{'walk'} are allowed. Are there any differences?


UPDATE: I noticed &{ 'run' } calls run(), while defined/undef &{ 'walk' } never call walk(). I think that's the difference. PBP written by D. Conway says "18.7 Always use strict". In this section, \&{$DUMP} doesn't violate "strict refs" because the expression doesn't call dump_at(). I thank PBP :-)

NOTE: PBP says "Never use symbolic references". This practice is undoubtedly reasonable.

In reply to undef/defined &{$name} while "strict refs" by anazawa

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, 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, 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.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others examining the Monastery: (5)
    As of 2018-01-23 12:04 GMT
    Find Nodes?
      Voting Booth?
      How did you see in the new year?

      Results (244 votes). Check out past polls.