Why is Perl foreach variable assignment modifying the values in the array?

Question

OK, I have the following code:

use strict;
my @ar = (1, 2, 3);
foreach my $a (@ar)
{
  $a = $a + 1;
}

print join \", \", @ar;

and the outp

Answer 1

the important distinction here is that when you declare a my variable in the initialization section of a for loop, it seems to share some properties of both locals and lexicals (someone with more knowledge of the internals care to clarify?)

my @src = 1 .. 10;

for my $x (@src) {
    # $x is an alias to elements of @src
}

for (@src) {
    my $x = $_;
    # $_ is an alias but $x is not an alias
}

the interesting side effect of this is that in the first case, a sub{} defined within the for loop is a closure around whatever element of the list $x was aliased to. knowing this, it is possible (although a bit odd) to close around an aliased value which could even be a global, which I don't think is possible with any other construct.

our @global = 1 .. 10;
my @subs;
for my $x (@global) { 
    push @subs, sub {++$x}
}

$subs[5](); # modifies the @global array