Module Design and Implementation

Here's an example of creating accessor mutators on demand using AUTOLOAD():

package BOA::Logger;

use Carp;

# initialize hash of attribute names

%ATTRIBUTES = map { $_ => 1 } qw(filename level format);

sub AUTOLOAD {

  return if $AUTOLOAD =~ /DESTROY$/;    # skip calls to DESTROY()

  my ($name) = $AUTOLOAD =~ /([^:]+)$/; # extract method name

  # check that this is a valid accessor call

  croak("Unknown method  $AUTOLOAD  called ") unless $ATTRIBUTES{$name};

  # create the accessor mutator and install it as &$name

  *$name = sub {

    my $self = shift;

    $self >{$name} = shift if @_;

    return $self >{$name};

  };

  goto &$name;  # jump to the new method with the magic goto(&) call

}

This code is more complicated than just creating all the accessors upfront, but if 

you have many attributes that are rarely called, it might be more efficient. Notice 

that AUTOLOAD() will only be called on the first call to each accessor; after that the 

newly created subroutine is installed and will be called directly. You might be 

tempted to skip this step and simply do the access directly in the AUTOLOAD() method, 

but this will slow your module significantly since Perl will spend time checking for 

the missing method every time the accessor is called.

Either of the preceding options is a clean way of auto generating methods.

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However, they require you to do some unnecessary work, which no doubt offends 

your instincts as a Perl programmer. It's unnecessary because there are two excellent 

modules Class::Struct and Class::MethodMaker that use similar techniques 

but provide a much more convenient interface. As a bonus, they also handle 

writing those repetitive constructors too!

8. And efficient too all the generated closures share the same compiled code.

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