my @employees; # Defined elsewhere as array of Employee objects
my $effect = Effect->new;
$effect->set( salary => 1.02, '*' );
$_->apply_effect( $effect ) for @employees;

##</code><code>##

my @employees; # Defined elsewhere as array of Employee objects
$_->salary( $_->salary() * 1.02 ) for @employees;

##</code><code>##

my $effect = Effect->new( [ salary => 1.02, '*' ] );

##</code><code>##

my @employess; # Defined elsewhere
my $effect = Effect->new(
    [ salary    => 1.02, '*' ],
    [ frobnitz  => 1.5, '+'  ],
);
$_->apply_effect( $effect ) for @employees;

##</code><code>##

my @employees; # Defined elsewhere
for (@employees) {
    $_->salary(    $_->salary() * 1.02 );
    $_->frobnitz(  $_->frobnitz + 1.5  );
}

# Or if you want to keep closer to the old code and 
# live with O(2n) . . . 
$_->salary(    $_->salary() * 1.02 ) for @employees;
$_->frobnitz(  $_->frobnitz + 1.5  ) for @employees;

##</code><code>##

my $do_operation; # Defined elsewhere, possibly from user input
my $by_ammount; # Also from user
my @employees; # Also defined elsewhere
my $op = 
    $do_operation eq 'add'   ? '+' :
    $do_operation eq 'mult'  ? '*' : 
    # And so on
;
my $effect = Effect->new( [ salary => $by_ammount, $op ] );
$_->apply_effect( $effect ) for @employees;