Set::Object(3)

NAME
Set::Object - set of objects and strings

SYNOPSIS
  use Set::Object qw(set);

  my $set = set();            # or Set::Object->new()

  $set->insert(@thingies);
  $set->remove(@thingies);

  @items = @$set;             # or $set->members for the unsorted array

  $union = $set1 + $set2;
  $intersection = $set1 * $set2;
  $difference = $set1 - $set2;
  $symmetric_difference = $set1 % $set2;

  print "set1 is a proper subset of set2"
      if $set1 < $set2;

  print "set1 is a subset of set2"
      if $set1 <= $set2;

  # common idiom - iterate over any pure Perl structure
  use Set::Object qw(reftype);
  my @stack = $root;
  my $seen = Set::Object->new(@stack);
  while (my $object = pop @stack) {
      if (reftype $object eq "HASH") {
          # do something with hash members

          # add the new nodes to the stack
          push @stack, grep { ref $_ && $seen->insert($_) }
              values %$object;
      }
      elsif (reftype $object eq "ARRAY") {
          # do something with array members

          # add the new nodes to the stack
          push @stack, grep { ref $_ && $seen->insert($_) }
              @$object;

      }
      elsif (reftype $object =~ /SCALAR|REF/) {
          push @stack, $$object
              if ref $$object && $seen->insert($$object);
      }
  }

DESCRIPTION
This modules implements a set of objects, that is, an unordered collection of objects without duplication.

The term objects is applied loosely - for the sake of Set::Object, anything that is a reference is considered an object.

Set::Object 1.09 and later includes support for inserting scalars (including the empty string, but excluding "undef") as well as objects. This can be thought of as (and is currently implemented as) a degenerate hash that only has keys and no values. Unlike objects placed into a Set::Object, scalars that are inserted will be flattened into strings, so will lose any magic (eg, tie) or other special bits that they went in with; only strings come out.

CONSTRUCTORS

  Set::Object->new( [list] )
Return a new "Set::Object" containing the elements passed in list.

  set(@members)
Return a new "Set::Object" filled with @members. You have to explicitly import this method.

New in Set::Object 1.22: this function is now called as a method to return new sets the various methods that return a new set, such as "->intersection", "->union", etc and their overloaded counterparts. The default method always returns "Set::Object" objects, preserving previous behaviour and not second guessing the nature of your derived Set::Object class.

  weak_set()
Return a new "Set::Object::Weak", filled with @members. You have to explicitly import this method.

INSTANCE METHODS

  insert( [list] )
Add items to the "Set::Object".

Adding the same object several times is not an error, but any "Set::Object" will contain at most one occurrence of the same object.

Returns the number of elements that were actually added. As of Set::Object 1.23, "undef" will not insert.

  includes( [list] )

  has( [list] )

  contains( [list] )
Return "true" if all the objects in list are members of the "Set::Object". list may be empty, in which case "true" is always returned.

As of Set::Object 1.23, "undef" will never appear to be present in any set (even if the set contains the empty string). Prior to 1.23, there would have been a run-time warning.

  member( [item] )

  element( [item] )
Like "includes", but takes a single item to check and returns that item if the value is found, rather than just a true value.

  members

  elements
Return the objects contained in the "Set::Object" in random (hash) order.

Note that the elements of a "Set::Object" in list context are returned sorted - @$set - so using the "members" method is much faster.

  size
Return the number of elements in the "Set::Object".

  remove( [list] )

  delete( [list] )
Remove objects from a "Set::Object".

Removing the same object more than once, or removing an object absent from the "Set::Object" is not an error.

Returns the number of elements that were actually removed.

As of Set::Object 1.23, removing "undef" is safe (but having an "undef" in the passed in list does not increase the return value, because it could never be in the set)

  weaken
Makes all the references in the set "weak" - that is, they do not increase the reference count of the object they point to, just like Scalar::Util's "weaken" function.

This was introduced with Set::Object 1.16, and uses a brand new type of magic. Use with caution. If you get segfaults when you use "weaken", please reduce your problem to a test script before submission.

New: as of Set::Object 1.19, you may use the "weak_set" function to make weak sets, or "Set::Object::Weak->new", or import the "set" constructor from "Set::Object::Weak" instead. See Set::Object::Weak for more.

Note to people sub-classing "Set::Object": this method re-blesses the invocant to "Set::Object::Weak". Override the method "weak_pkg" in your sub-class to control this behaviour.

  is_weak
Returns a true value if this set is a weak set.

  strengthen
Turns a weak set back into a normal one.

Note to people sub-classing "Set::Object": this method re-blesses the invocant to "Set::Object". Override the method "strong_pkg" in your sub-class to control this behaviour.

  invert( [list] )
For each item in list, it either removes it or adds it to the set, so that a change is always made.

Also available as the overloaded operator "/", in which case it expects another set (or a single scalar element), and returns a new set that is the original set with all the second set's items inverted.

  clear
Empty this "Set::Object".

  as_string
Return a textual Smalltalk-ish representation of the "Set::Object". Also available as overloaded operator "".

  equal( set )
Returns a true value if set contains exactly the same members as the invocant.

Also available as overloaded operator "==" (or "eq").

  not_equal( set )
Returns a false value if set contains exactly the same members as the invocant.

Also available as overloaded operator "!=" (or "ne").

  intersection( [list] )
Return a new "Set::Object" containing the intersection of the "Set::Object"s passed as arguments.

Also available as overloaded operator "*".

  union( [list] )
Return a new "Set::Object" containing the union of the "Set::Object"s passed as arguments.

Also available as overloaded operator "+".

  difference ( set )
Return a new "Set::Object" containing the members of the first (invocant) set with the passed "Set::Object"s' elements removed.

Also available as overloaded operator "-".

  unique ( set )

  symmetric_difference ( set )
Return a new "Set::Object" containing the members of all passed sets (including the invocant), with common elements removed. This will be the opposite (complement) of the intersection of the two sets.

Also available as overloaded operator "%".

  subset( set )
Return "true" if this "Set::Object" is a subset of set.

Also available as operator "<=".

  proper_subset( set )
Return "true" if this "Set::Object" is a proper subset of set Also available as operator "<".

  superset( set )
Return "true" if this "Set::Object" is a superset of set. Also available as operator ">=".

  proper_superset( set )
Return "true" if this "Set::Object" is a proper superset of set Also available as operator ">".

  is_null( set )
Returns a true value if this set does not contain any members, that is, if its size is zero.

Set::Scalar compatibility methods
By and large, Set::Object is not and probably never will be feature-compatible with Set::Scalar; however the following functions are provided anyway.

  compare( set )
returns one of:

  "proper intersect"
  "proper subset"
  "proper superset"
  "equal"
  "disjoint"

  is_disjoint( set )
Returns a true value if the two sets have no common items.

  as_string_callback( set )
Allows you to define a custom stringify function. This is only a class method. If you want anything fancier than this, you should sub-class Set::Object.

FUNCTIONS
The following functions are defined by the Set::Object XS code for convenience; they are largely identical to the versions in the Scalar::Util module, but there are a couple that provide functions not catered to by that module.

Please use the versions in Scalar::Util in preference to these functions. In fact, if you use these functions in your production code then you may have to rewrite it some day. They are retained only because they are "mostly harmless".

blessed
    Do not use in production code

    Returns a true value if the passed reference (RV) is blessed. See also Acme::Holy.

reftype
    Do not use in production code

    A bit like the perl built-in "ref" function, but returns the type of reference; ie, if the reference is blessed then it returns what "ref" would have if it were not blessed. Useful for "seeing through" blessed references.

refaddr
    Do not use in production code

    Returns the memory address of a scalar. Warning: this is not guaranteed to be unique for scalars created in a program; memory might get re-used!

is_int, is_string, is_double
    Do not use in production code

    A quick way of checking the three bits on scalars - IOK (is_int), NOK (is_double) and POK (is_string). Note that the exact behaviour of when these bits get set is not defined by the perl API.

    This function returns the "p" versions of the macro (SvIOKp, etc); use with caution.

is_overloaded
    Do not use in production code

    A quick way to check if an object has overload magic on it.

ish_int
    Deprecated and will be removed in 2014

    This function returns true, if the value it is passed looks like it already is a representation of an integer. This is so that you can decide whether the value passed is a hash key or an array index.

is_key
    Deprecated and will be removed in 2014

    This function returns true, if the value it is passed looks more like an index to a collection than a value of a collection. Similar to the looks_like_number internal function, but weird. Avoid.

get_magic
    Do not use in production code

    Pass to a scalar, and get the magick wand ("mg_obj") used by the weak set implementation. The return will be a list of integers which are pointers to the actual "ISET" structure. Whatever you do don't change the array :). This is used only by the test suite, and if you find it useful for something then you should probably conjure up a test suite and send it to me, otherwise it could get pulled.

CLASS METHODS
These class methods are probably only interesting to those sub-classing "Set::Object".

strong_pkg
    When a set that was already weak is strengthened using "->strengthen", it gets re-blessed into this package.

weak_pkg
    When a set that was NOT already weak is weakened using "->weaken", it gets re-blessed into this package.

tie_array_pkg
    When the object is accessed as an array, tie the array into this package.

tie_hash_pkg
    When the object is accessed as a hash, tie the hash into this package.

SERIALIZATION
It is possible to serialize "Set::Object" objects via Storable and duplicate via "dclone"; such support was added in release 1.04. As of "Set::Object" version 1.15, it is possible to freeze scalar items, too.

However, the support for freezing scalar items introduced a backwards incompatibility. Earlier versions than 1.15 will "thaw" sets frozen using Set::Object 1.15 and later as a set with one item - an array that contains the actual members.

Additionally, version 1.15 had a bug that meant that it would not detect "freeze" protocol upgrades, instead reverting to pre-1.15 behaviour.

"Set::Object" 1.16 and above are capable of dealing correctly with all serialized forms, as well as correctly aborting if a "newer" "freeze" protocol is detected during "thaw".

PERFORMANCE
The following benchmark compares "Set::Object" with using a hash to emulate a set-like collection (this is an old benchmark, but still holds true):

   use Set::Object;

   package Obj;
   sub new { bless { } }

   @els = map { Obj->new() } 1..1000;

   require Benchmark;

   Benchmark::timethese(100, {
      'Control' => sub { },
      'H insert' => sub { my %h = (); @h{@els} = @els; },
      'S insert' => sub { my $s = Set::Object->new(); $s->insert(@els) },
      } );

   %gh = ();
   @gh{@els} = @els;

   $gs = Set::Object->new(@els);
   $el = $els[33];

   Benchmark::timethese(100_000, {
           'H lookup' => sub { exists $gh{33} },
           'S lookup' => sub { $gs->includes($el) }
      } );

On my computer the results are:

   Benchmark: timing 100 iterations of Control, H insert, S insert...
      Control:  0 secs ( 0.01 usr  0.00 sys =  0.01 cpu)
               (warning: too few iterations for a reliable count)
     H insert: 68 secs (67.81 usr  0.00 sys = 67.81 cpu)
     S insert:  9 secs ( 8.81 usr  0.00 sys =  8.81 cpu)
   Benchmark: timing 100000 iterations of H lookup, S lookup...
     H lookup:  7 secs ( 7.14 usr  0.00 sys =  7.14 cpu)
     S lookup:  6 secs ( 5.94 usr  0.00 sys =  5.94 cpu)

This benchmark compares the unsorted members method, against the sorted @$ list context.

   perl -MBenchmark -mList::Util -mSet::Object -e'
   $set = Set::Object::set (List::Util::shuffle(1..1000));
   Benchmark::timethese(-3, {
      "Slow \@\$set       " => sub { $i++ for @$set; },
      "Fast set->members" => sub { $i++ for $set->members(); },
      });'

    Benchmark: running Fast set->members, Slow @$set        for at least 3 CPU seconds...
    Fast set->members:  4 wallclock secs ( 3.17 usr +  0.00 sys =  3.17 CPU) @ 9104.42/s (n=28861)
    Slow @$set       :  4 wallclock secs ( 3.23 usr +  0.00 sys =  3.23 CPU) @ 1689.16/s (n=5456)

THREAD SAFETY
This module is not thread-safe.

AUTHOR
Original Set::Object module by Jean-Louis Leroy, <jll@skynet.be>

Set::Scalar compatibility, XS debugging, weak references support courtesy of Sam Vilain, <samv@cpan.org>.

New maintainer is Reini Urban <rurban@cpan.org>. Patches against <https://github.com/rurban/Set-Object/> please. Tickets at RT <https://rt.cpan.org/Public/Dist/Display.html?Name=Set-Object>

LICENCE
Copyright (c) 1998-1999, Jean-Louis Leroy. All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the terms of the Perl Artistic License, either the original, or at your option, any later version.

Portions Copyright (c) 2003 - 2005, Sam Vilain. Same license.

Portions Copyright (c) 2006, 2007, Catalyst IT (NZ) Limited. This module is free software. It may be used, redistributed and/or modified under the terms of the Perl Artistic License

Portions Copyright (c) 2013, cPanel. Same license. Portions Copyright (c) 2020, Reini Urban. Same license.

SEE ALSO
perl(1), perltie(1), Set::Scalar, overload