Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Interesting. I knew that some builtins, like pos and keys, can be lvalues, but not that arguments to subs were. Come to think of it, I can't even say that I know what the expression "arguments to subs are lvalues" means. How is the argument in sleep( 3 ) an lvalue? Arguments to subs can be assigned to; they're lvalues in that sense. Therefore, you get these ugly situations:
my $var=3; mysleep($var); # these two lines are fine mysleep(3); # but this one causes an error!!! sub mysleep { sleep($_[0]); $_[0]=10; }
Or this ugly situation...:
$y=substr("hello",10,1); foo($y);# this runs, but substr() generates warnings because the subst +r() is outside the string foo( substr("hello",10,1) ); # this is a fatal error!

Why is it a fatal error? Well, because an invalid substr() is used in a lvalue context. Why is it an lvalue context? Because the subroutine *could* modify the value, and perl isn't smart enough to check to see if it does or not! Worse yet, substr() fails silently on such a fatal error, after generating the *same* warning that's nonfatal in a non-lvalue context. ***SIGH***

I've made it my policy to avoid lvalues() where possible, especially after that substr() issue killed our production code, and wasted a few hours of my time! --
Ytrew Q. Uiop

In reply to Re^3: Autovivification of scalars in sub calls by Anonymous Monk
in thread Autovivification of scalars in sub calls by tlm

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 the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others rifling through the Monastery: (6)
    As of 2019-07-19 20:48 GMT
    Find Nodes?
      Voting Booth?

      No recent polls found