use strict;
use warnings;
use Scalar::Util qw(looks_like_number);


#-- Common helper
sub mul_if_num {
  my ($expr, $factor) = @_;
  return looks_like_number( $expr ) ?  $factor * $expr : $expr;
}


#-- Cool1: Overloading
{
package ArrayMul;
use overload '*=' => \&mulby;

sub new {
  my $self = shift;
  return bless [ @_ ],  __PACKAGE__;
}

sub mulby {
  my ($self, $factor, $swap) = @_;
  @$self = map{ main::mul_if_num( $_, $factor ) } @$self;
  return $self;
}

1;
}

package main;

#-- Cool2: hide loop in sub - profit from re-use and readability
sub scalar_mul {
  my ($aref, $factor) = @_;
  #TODO: parameter checks (2 params, first is ref, second is scalar)
  $_ = mul_if_num( $_, $factor ) for @{$aref};
  die 'ill. context' if defined wantarray;
}

#-- Examples
my @array  = qw(1 2 3 4 what? +1 -7 666+666);
my $array2 = ArrayMul->new( @array );
my @array3 = @array;
my @array4 = @array;

#-- Cool1! but no @-sigil. Unexpected side-effects likely.
$array2 *= 2;

#-- Cool2! loop hidden elsewhere
scalar_mul( \@array3, 3 );

#-- Cool3! but creates new array
use List::MoreUtils qw(apply);
@array4 =  apply { $_ = mul_if_num( $_, 4 ) } @array;

#-- Results
print "@{$_}\n"  for ( \@array, $array2 ,\@array3 , \@array4);

__END__

1 2 3 4 what? +1 -7 666+666
2 4 6 8 what? 2 -14 666+666
3 6 9 12 what? 3 -21 666+666
4 8 12 16 what? 4 -28 666+666