"..an "inside-out" version of foreach."

That's a handy way of looking at map.

I'm not so sure about:

DO_SOMETHING_WITH-$_
[download]

In both cases you would be changing the array. Indeed it would only work with an array (see the comment below). This is clearly your intention with the map as you've used it in void context, i.e. although map returns a list you're just throwing it away.

It may be better to say map is useful if you want to create an array based on another array. I think: "Do something with a $_, but don't change it" would be better/safer. :-)

#!/usr/bin/perl 

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


my @array = qw{a b c};
my @new_array = map{my $letter = $_; ++$letter} @array;
print "before: @array\n";
print "after:  @new_array\n";

# with some extra white space
# it looks even more 'inside-out' :-)
my @another = map{
  my_func()
} @new_array;

print "another: @another\n";
print "original \@array: @array\n";



sub my_func {
  my $letter = $_;
  $letter++;
  return $letter;
}

exit;

# DO_SOMETHING_WITH-$_
# doesn't work on a list
for (qw{a b c}){
  # this line generates:
  # "Modification of a read-only value attempted at..."
  ++$_;
}

# so does this
map {++$_} qw{a b c};
[download]

output:

---------- Capture Output ----------
> "C:\Perl\bin\perl.exe" _new.pl

before: a b c
after:  b c d
another: c d e
original @array: a b c

> Terminated with exit code 0.
[download]

updated: corrected my_func sub.

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