The fewer parameters that you pass to a subroutine, the easier it tends to be to maintain (assuming that everything is nicely encapsulated and you're not using globals or something like that). This is because the logic of dealing with one variable is typically going to be simpler than the logic of dealing with multiple variables. However, if I must pass numerous parameters, I like to set a threshhold of say, 4 parameters, and switch to a named argument style.

Consider the following, which is easy to happen when reusing a lot of code:

some_func( $foo, $bar, $baz, $qux );

# in another program

some_func( $w, $x, $y, $z );

# yet another program

some_func( $amount, $rate, $limit, $exception );
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With this, not only are you forced to pass multiple parameters (even if they are undef), but you have to remember the order of the parameters. This can be awkward. Hmm... do I have the third and fourth parameters reversed, or not? However, what if $limit is optional, and I can't remember the order of $rate and $exception? With named parameters, this is a moot point:

some_func( 
    exception => $exception,
    amount    => $amount,
    rate      => $rate
);
[download]

Cheers,
Ovid

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