Re^6: Use of "my" after Perl v5.14

[AnomalousMonk]

use v5.14;

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

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

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

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.