foreach causes $color to be an alias for $colors[0], $colors[1], and $colors[2]. In other words, if you were to assign "pink" to $color on each iteration through the loop, @colors would be filled with 'pink', 'pink', and 'pink'. But the lexical $color, outside of the loop, would remain undefined. This is because of the fact that $color, inside the loop, is a localized alias to the elements of the list you're iterating over. It just happens to be localizing the lexical $color. But when the loop exits, the localized effects are dropped, and $color reverts back to its original self.

The subroutine is defined outside of the loop, and therefore sees the version of $color that exists outside of the loop, and doesn't know about the localized aliases that are taking place inside the loop.

This is a somewhat sloppy version of a closure.

The proper way to pass data into a subroutine is as a parameter. You will find that if you rewrite your snippet with that in mind, your results will be more in keeping with what you predict them to be. 

use strict;

my @colors = qw ( red green blue );

my $color;  
my $light = 'on';

foreach $color (@colors) {
    print "\$color is '$color' and \$light is '$light' in loop, ";
    print_color( $color, $light );
}

####
sub print_color {
    my ( $clr, $lite ) = @_;
    print " in sub values are '$clr' and '$lite'\n";
}

[download]

Also, if you want to preserve the last value of the loops iterator variable, you should play it safe by copying it to a variable that exists at greater scope, that hasn't been a part of the localized aliasing process.


Dave

In reply to Re: strict, scope, my and foreach - not behaving as expected by davido
in thread strict, scope, my and foreach - not behaving as expected by queeg

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