# NAME

Set::Light - (memory efficient) unordered set of strings

# VERSION

version 0.90

# SYNOPSIS

```perl
    use Set::Light;

    my $set = Set::Light->new( qw/foo bar baz/ );

    if (!$set->is_empty())
      {
      print "Set has ", $set->size(), " elements.\n";
      for (qw/umpf foo bar baz bam/)
        {
        print "Set does ";
        print " not " unless $set->has($_);
        print "contain '$_'.\n";
        }
      }
```

# DESCRIPTION

Set::Light implements an unordered set of strings. Set::Light currently
uses underneath a hash, and each key of the hash points to the same
scalar, thus saving memory per item.

## Why not use a hash?

Usually you would use a hash to keep track of a list of items like:

```perl
    my %SEEN;
    ...
    if (!$SEEN->{$item}++)
      {
      # haven't seen item before
      }
```

While this is very fast (both on inserting items, as well as looking them up),
it wastes quite a lot of memory, since each key in %SEEN needs one scalar.

## Why not use Set::Object or Set::Scalar?

These waste even more memory and/or are slower than an ordinary hash.

# TYPES

## new()

```perl
    my $set = Set::Light->new();
```

Creates a new Set::Light object. An optionally passed hash reference can
contain options. Currently no options are supported:

```perl
    my $set = Set::Light->new( { myoption => 1, foobar => 2 });
```

Note that:

```perl
    my $set = Set::Light->new( qw/for bar baz/);
```

will create a set with the members `for`, `bar` and `baz`.

## size()

```perl
    my $elems = $set->size();
```

Returns the number of elements in the set.

## is\_empty()

```
    if (!$set->is_empty()) { ... }
```

Returns true if the set is empty (has zero elements).

## is\_null()

`is_null()` is an alias to `is_empty()`.

## has()/contains()/exists/()

```
    if ($set->has($member)) { ... }
```

Returns true if the set contains the string `$member`.

`contains()` and `exists()` are aliases to `has()`.

## insert()

```
    $set->insert( $string );
    $set->insert( @strings );
```

Inserts one or more strings into the set. Returns the number of insertions
it really did. Elements that are already contained in the set do not
get inserted twice. So:

```perl
    use Set::Light;
    my $set = Set::Light->new();
    print $set->insert('foo');              # 1
    print $set->insert('foo');              # 0
    print $set->insert('bar','baz','foo');  # 2     (foo already inserted)
```

## delete()/remove()

```
    $set->delete( $string );
    $set->delete( @strings );
```

Deletes one or more strings from the set. Returns the number of deletions
it really did. Elements that are not contained in the set cannot be deleted.
So:

```perl
    use Set::Light;
    my $set = Set::Light->new();
    print $set->insert('foo','bar');        # 2
    print $set->delete('foo','foo');        # 1     (only once deleted)
    print $set->delete('bar','foo');        # 1     (only once deleted)
```

`remove()` is an alias for `delete()`.

# SEE ALSO

[Set::Object](https://metacpan.org/pod/Set::Object), [Set::Scalar](https://metacpan.org/pod/Set::Scalar).

# SOURCE

The development version is on github at [https://github.com/robrwo/Set-Light](https://github.com/robrwo/Set-Light)
and may be cloned from [git://github.com/robrwo/Set-Light.git](git://github.com/robrwo/Set-Light.git)

# BUGS

Please report any bugs or feature requests on the bugtracker website
[https://rt.cpan.org/Public/Dist/Display.html?Name=Set-Light](https://rt.cpan.org/Public/Dist/Display.html?Name=Set-Light) or by email
to [bug-Set-Light@rt.cpan.org](mailto:bug-Set-Light@rt.cpan.org).

When submitting a bug or request, please include a test-file or a
patch to an existing test-file that illustrates the bug or desired
feature.

# AUTHOR

Tels <nospam-abuse@bloodgate.com>

# CONTRIBUTOR

Robert Rothenberg <rrwo@cpan.org>

# COPYRIGHT AND LICENSE

This software is copyright (c) 2004-2008, 2019 by Tels.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.