adaughterson has asked for the wisdom of the Perl Monks concerning the following question:

Greetings exalted ones:

I feel like I'm missing something really obvious here, but when I try to move my custom sort method into the base class, $a and $b don't magically appear like when the sort method is contained within the current context, or inline.

Is it even possible to use an inherited method for my custom sort? Thanks, Adam

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Re: Inherit custom sort method from base class
by vsespb (Chaplain) on Oct 01, 2013 at 22:01 UTC
    Sort comparison function should be a.. function, not a method.

    Thus I don't quite understand how class inheritance applies here.

    Would you mind simplifying your code to proof-of-concept example and posting here so we would see the problem?
[reply]

      I can certainly do that.

      The base-class: 
      Package MyBaseClass;

sub new
{
  my $class = shift;
  my $self = {};
  bless($self,$class);
  $self->_init();
  return $self;
}

sub _init
{
  my $self = shift;
  @{$self->{things}} = qw(thing_0.1 thing_0.2 thing_0.3 thing_11.0 thi
+ng_11.1);
  # etc,etc
  return $self;
}

# $a and $b don't seem to exist within this context
sub specialSort
{
  my $self = shift;
  my @aParts = split(/[_.]/, $a);
  my @bParts = split(/[_.]/, $b);
  return 1 if (int $a_parts[1] > int $b_parts[1] || ($a_parts[1] eq $b
+_parts[1] && (int $a_parts[2]) > (int $b_parts[2])));
  return -1 if (int $a_parts[1] < int $b_parts[1] || ($a_parts[1] eq $
+b_parts[1] && (int $a_parts[2]) < (int $b_parts[2])));          
  return 0 if ($a eq $b);
  die((caller(0))[3] . " LOGIC error.");
}

1;

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      The subclass: 
      package MySubclass;
require MyBaseClass;
our @ISA = qw(MyBaseClass);

sub new
{
  my $class = shift;
  my $self = {};
  bless($self,$class);
  $self->_init();
  return $self;
}

sub _init
{
  my $self = shift;
  MyBaseClass::_init($self);
  return $self;
}

sub doSomething
{
  my $self = shift;

  # this works
  foreach my $thing(sort specialSort @{$self->{things}})
  {
    # do something with $thing...
  }

  # this doesn't work
  foreach my $thing(sort $self->specialSort @{$self->{things}})
  {
    # do something with $thing...
  }
}

sub specialSort
{
  # Notice that there is no 'my $self = shift' here...
  my @aParts = split(/[_.]/, $a);
  my @bParts = split(/[_.]/, $b);
  return 1 if (int $a_parts[1] > int $b_parts[1] || ($a_parts[1] eq $b
+_parts[1] && (int $a_parts[2]) > (int $b_parts[2])));
  return -1 if (int $a_parts[1] < int $b_parts[1] || ($a_parts[1] eq $
+b_parts[1] && (int $a_parts[2]) < (int $b_parts[2])));          
  return 0 if ($a eq $b);
  die((caller(0))[3] . " LOGIC error.");
}

1;

      [download]
[reply]
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[select]
        Try 
        sort { $self->specialSort($a, $b) } @{$self->{things}})

        [download]
        and remove specialSort from MySubclass.
        you have to use 1st and 2nd arguments instead of $a and $b in base class' specialSort

        You cannot use $self->specialSort as subroutine name, so you have to use new "subroutine": 
        { $self->specialSort($a, $b) }

        [download]

        Also, technically, you can put 
        use base qw/Exporter/;
@EXPORT = qw/specialSort/;

        [download]

        into base class,
        then remove specialSort from MySubclass, and then it will work.
        but it's probably bad style to mix inheritance and exported functions.

        UPD: fixed $a,$b in code
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