What does the following code do? 

my $effect = Effect->new;
$effect->set( salary => 1.02, '*' ); # A 2% raise
$employee->apply_effect( $effect );

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All one can say it that it might raise the salary by 2% or it might do nothing at all, not even report an error. So now we have a Perl that doesn't give you compile time checking and doesn't give you run time checking either!

The exact same effect can be achieved by having all your objects inherit from a base class with 

sub AUTOLOAD {
# do nothing
}

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then go back to using 
$employee->salary(  $employee->salary * 1.02  );

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Yes this would be an incredibly bad idea but it's exactly equivalent to using effect objects and it's a hell of a lot easier.

There are some times when you want missing fields to be ignored but you should make that explicit in your code by doing something like 

$employee->salary(  $employee->salary * 1.02  );
# we don't mind if they don't have a frobnitz
eval { $employee->frobnitz(  $employee->frobnitz + 1.5  ) };

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Problems with effect objects

The only real use I can think of for an effect object is to use it as a callback mechanism. Various people can add effects (or even remove or reorder effects) as the object is passed around, but I still don't see a reason to make it ignore errors by default.

In reply to Re^12: Assignable Subroutines by fergal
in thread Assignable Subroutines by dragonchild

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