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The following page has been changed by JustinMason:
http://wiki.apache.org/spamassassin/PerlAccessorsConsideredHarmful

New page:
= Perl-Style Accessors Considered Harmful =

(a quick break-out page from the 'Accessors' section of CodingStyle).

We don't use traditional perl-style variable accessor methods very frequently
(ie.

{{{
sub foo {
my ($self, $val) = @_;
if (defined $val) {
$self->{foo} = $val;
} else {
return $val;
}
}
}}}

Instead, the more wordy Java/C++ style is preferred:

{{{
sub get_foo {
my ($self) = @_;
return $val;
}
sub set_foo {
my ($self, $val) = @_;
$self->{foo} = $val;
}
}}}

The perl style is considered a bad idea, because it can become a
no-op, if the value being passed in is 'undef'. Here's how:

* Let's say you have a perl-style accessor {{{$self->foo()}}}, which is used to access the value {{{$self->{foo}}}}.
* {{{$self->{foo}}}} is currently eq {{{'bar'}}}.
* A caller comes along with a variable $_, and wants to set the foo value to whatever's in $_. They therefore call {{{$self->foo($_)}}}.
* ''The bug:'' if $_ is undef, that means that {{{$self->foo(undef)}}} is called. In a perl-style accessor, that is considered a 'get' operation instead of a 'set', so after that call, $self->{foo} is still set to {{{'bar'}}}.

This has bitten us in the past.

In the Java-style accessor, the source code itself mandates whether the
operation is a set or a get; the data cannot affect which operation happens.
Hence, it's safer.