Why don't I get a warning when I redeclare the Perl foreach control variable?

Question

Why is there no warning thrown for the redeclaration of $i in the following code?

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

         


        

Answer 1

Actually, you only get warnings for redefinitions in the same scope. Writing:

use warnings;
my $i;
{
  my $i;
  # do something to the inner $i
}
# do something to the outer $i

is perfectly valid.

I am not sure if the Perl internals handle it this way, but you can think of your for loop as being parsed as

{
  my $i;
  for $i ( ... ) { ... }
  # the outer scope-block parens are important!
};

Answer 2

You would get a warning if you redeclare a my, our or state variable in the current scope or statement. The first $i isn't actually a lexical variable. You can prove this using Devel::Peek:

use Devel::Peek;   

for my $i (1) {
    Dump $i;
}  

SV = IV(0x81178c8) at 0x8100bf8
REFCNT = 2
FLAGS = (IOK,READONLY,pIOK)
IV = 1

There's no PADMY flag in FLAGS, which would indicate that $i is a lexical variable, declared with my.