Question

From perldoc perlsyn on the topic of Foreach Loops:

If the variable was previously
declared with my, it uses that
variable instead of the global one,
but it’s still localized to the loop.

But consider this example:

use Devel::Peek;
my $x = 1;
Dump $x;
for $x ( 1 ) { Dump $x }

SV = IV(0x8117990) at 0x8100bd4
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,IOK,pIOK)
  IV = 1
SV = IV(0x8117988) at 0x8100bf8
  REFCNT = 2
  FLAGS = (IOK,READONLY,pIOK)
  IV = 1

It seems like these are not the same variables. Is it an error in docs, or am I missing anything?

Answer 1

Every rule needs its exception, and this is one. In a for loop, if the loop variable is a lexical (declared with my), Perl will create a new lexical aliased to the current item in the loop. The OP code could be written as follows:

use Data::Alias 'alias';

my $x = 1;
for (2..3) {
    alias my $x = $_;
    # note that $x does not have dynamic scope, and will not be visible in 
    # subs called from within the loop
    # but since $x is a lexical, it can be closed over
}

Edit: previous example was in Perl pseudocode, answer revised for clarity.