[Spamassassin Wiki] Update of "PerlAccessorsConsideredHarmful" by JustinMason

[Apache Wiki <wi...@apache.org>]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Spamassassin Wiki" for change notification.

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.