use v5.14;

{
    my $count = 1;
    sub counter {
        say $count++;
    }
}

counter();
counter();
counter();
counter();

[download]

Unfortunately, this approach hides a subtle pitfall — well, subtle enough, at any rate, to catch me more than once. The problem is here illustrated: 

>perl -wMstrict -le
"use v5.14;
 ;;
 counter();
 counter();
 ;;
 { my $count = 42;
   ;;
   sub counter { say $count++; }
   }
 ;;
 counter();
 counter();
"
0
1
42
43

[download]

There is a critical dependence upon order of execution. The  $count lexical variable is created at compile time, so the  counter() function has no problem accessing it; the code runs with warnings and strictures fully enabled. The variable is not initialized within its closure until some moment during run time; this moment may precede or follow any invocation of the function that quite happily accesses the variable. KaBoom!

It's pretty easy to avoid this problem: perhaps the easiest way is to just use a state variable! But the first step toward avoidance is awareness.

In reply to Re^6: Use of "my" after Perl v5.14 by AnomalousMonk
in thread Use of "my" after Perl v5.14 by Rohit Jain

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.