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

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

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

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

my @employees; # Defined elsewhere
for (@employees) {
...
# live with O(2n) . . . 
$_->salary(    $_->salary() * 1.02 ) for @employees;
$_->frobnitz(  $_->frobnitz + 1.5  ) for @employees;

my $do_operation; # Defined elsewhere, possibly from user input
my $by_ammount; # Also from user
...
;
my $effect = Effect->new( [ salary => $by_ammount, $op ] );
$_->apply_effect( $effect ) for @employees;