http://www.perlmonks.org?node_id=1056542


in reply to Inherit custom sort method from base class

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?
  • Comment on Re: Inherit custom sort method from base class

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Re^2: Inherit custom sort method from base class
by adaughterson (Initiate) on Oct 01, 2013 at 22:23 UTC

    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;

    [download]
    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]
[d/l]
[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
[reply]
[d/l]
[select]

        Here's another, slightly different approach to what vsespb is talking about. (But I still don't understand how
            $self->specialSort(my ($a, $b))
        works!) 

        >perl -wMstrict -le
"{ package Base;
   ;;
   sub new {
     my $class = shift;
     return bless({} => $class)->init(@_);
     }
   ;;
   sub init {
     my $self = shift;
     @{ $self->{things} } = (qw(a E d Bee Z cee d C zee E eks), @_);
     return $self;
     }
   ;;
   sub print {
     my $self = shift;
     CORE::print qq{@{ $self->{things}} };
     }
   ;;
   sub nocase_descending {
     my $class_obj = shift;
     return lc($_[1]) cmp lc($_[0]);
     }
   ;;
   }
 ;;
 ;;
 { package Derived;
   use parent -norequire, qw(Base);
   ;;
   sub sort {
     my $self = shift;
     return
       CORE::sort { $self->nocase_descending($a, $b) }
       @{ $self->{things} }
       ;
     }
   ;;
   }
 ;;
 ;;
 my $d = Derived->new(qw(SS r QQ p PP q RR s));
 ;;
 $d->print;
 ;;
 my @sorted = $d->sort;
 print qq{@sorted};
 ;;
 @sorted = sort @{ $d->{things} };
 print qq{@sorted};
 ;;
 print $d;
"
a E d Bee Z cee d C zee E eks SS r QQ p PP q RR s
zee Z SS s RR r QQ q PP p eks E E d d cee C Bee a
Bee C E E PP QQ RR SS Z a cee d d eks p q r s zee
Derived=HASH(0x1e931f4)

        [download]

        Update: Moved  print method from  Derived class 'up' into  Base class (just because I can).

[reply]
[d/l]
[select]

        That worked great! Thanks for the assist :)

        sort { $self->specialSort(my ($a,$b)) } @{$self->{things}} # ...my, because use strict is in play
[reply]
[d/l]

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