- NAME
- SYNOPSIS
- EXPORTS
- DEPENDENCIES
- DESCRIPTION
- EXAMPLES
- PUBLIC INTERFACE

- new
- shift
- unshift
- push
- pop

- AUTHORS
- COPYRIGHT

# NAME

Data::CompositeHash -

--title=Data::CompositeHash

# SYNOPSIS

--title=Data::CompositeHash

# EXPORTS

Nothing exported by default

--title=Data::CompositeHash

# DEPENDENCIES

This module requires these other modules and libraries:

        Error::Simple
        Error::Programatic
        Perl::Module
        Data::Hub::Util
        Data::Hub::Container

--title=Data::CompositeHash

# DESCRIPTION

--title=Data::CompositeHash

# EXAMPLES

This example will not abort:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      # We now have a composite stack with prescedence: $h1, $h2, $h3
      # Where $h2 is the default hash
      $ch->{a} = 'AA';
      $ch->{b} = 'BB';
      $ch->{c} = 'CC';
      $ch->{d} = 'DD';
      die unless $h1->{a} eq 'AA';
      die unless $h2->{b} eq 'BB';
      die unless $h3->{c} eq 'CC';
      die unless $h2->{d} eq 'DD'; # set on default hash b/c 'd' did not exist

This example will not abort:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      # We now have a composite stack with prescedence: $h1, $h2, $h3
      # Where $h2 is the default hash
      die unless $ch->{a} eq 'a1';
      die unless $ch->{b} eq 'b2';
      die unless $ch->{c} eq 'c3';
      die unless ref($ch->{'/'});

This example:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      join '', sort values %$ch;

will return:

      a1b2c3

This example will not abort:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      die unless exists $$ch{a};
      die unless exists $$ch{b};
      die unless exists $$ch{c};
      die if exists $$ch{d};

This example:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      delete $ch->{a};
      delete $ch->{b};
      delete $ch->{c};
      join '', sort values %$ch;

will return:

      a2b3

This example:

      my $h1 = {a=>'a1'};
      my $h2 = {a=>'a2', b=>'b2'};
      my $h3 = {a=>'a3', b=>'b3', c=>'c3'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->unshift($h1);
      $ch->push($h3);
      %$ch = ();
      join '', sort values %$ch;

will return:

      a2b2

This example will return true:

      my $h2 = {a=>'a2', b=>'b2'};
      my $ch = Data::CompositeHash->new($h2);
      scalar(%$ch);

This example will return false:

      my $h2 = {a=>'a2', b=>'b2'};
      my $ch = Data::CompositeHash->new($h2);
      $ch->pop;
      scalar(%$ch);

This example:

      use Data::CompositeHash;
      my $h1 = {
        'a' => 'argon',
      };
      my $h2 = {
        'a' => 'apple',
        'b' => 'banana',
        'c' => 'cherry',
      };
      my $h3 = {
        'c' => 'cyan',
        'd' => 'dark brown',
      };
      my $result = '';
      # Create a composite hash, using $h2 as the default hash
      my $ch = Data::CompositeHash->new($h2);
      # Add $h1 as a hash which will overried values in $h2
      $ch->unshift($h1);
      # Add $h3 as a hash with the least prescedence
      $ch->push($h3);
      # Fetch some values
      $result .= $ch->{a} . "\n";
      $result .= $ch->{b} . "\n";
      $result .= $ch->{c} . "\n";
      $result .= $ch->{d} . "\n";
      # Set an ambiguous value
      $result .= "--\n";
      $ch->{a} = 'aluminium';
      $result .= $h1->{a} . "\n"; # contains new value
      $result .= $h2->{a} . "\n"; # not touched
      # Set an ambiguous value
      $result .= "--\n";
      $ch->{c} = 'cantelope';
      $result .= $h2->{c} . "\n"; # contains new value
      $result .= $h3->{c} . "\n"; # not touched
      # Setting a value which is not defined in any hash sets
      # it on the defalut hash
      $result .= "--\n";
      $ch->{e} = 'edible fruit';
      $result .= $h2->{e};

will return:

      argon
      banana
      cherry
      dark brown
      --
      aluminium
      apple
      --
      cantelope
      cyan
      --
      edible fruit

--title=Data::CompositeHash

# PUBLIC INTERFACE

## new

Create a new CompositeHash

  This example will not abort:

        use Data::CompositeHash;

  This example will abort:

        # no default hash provided
        my $ch = Data::CompositeHash->new();

## shift

Shift a hash from the composite stack

  This example will not return a defined value:

        my $h2 = {a=>'a2'};
        my $ch = Data::CompositeHash->new($h2);
        $ch->shift;
        $ch->{a};

## unshift

Unshift `hash(es)` on to the composite stack

  This example:

        my $h1 = {a=>'a1'};
        my $h2 = {a=>'a2'};
        my $ch = Data::CompositeHash->new($h2);
        $ch->unshift($h1);
        $ch->{a};

  will return:

        a1

## push

Push `hash(es)` on to the composite stack

  This example:

        my $h2 = {a=>'a2'};
        my $h3 = {a=>'a3'};
        my $ch = Data::CompositeHash->new($h2);
        $ch->push($h3);
        $ch->{a};

  will return:

        a2

## pop

Pop a hash off the composite stack

  This example will not return a defined value:

        my $h2 = {a=>'a2'};
        my $ch = Data::CompositeHash->new($h2);
        $ch->pop;
        $ch->{a};

--title=Data::CompositeHash

# AUTHORS

        Ryan Gies <ryangies@cpan.org>

--title=Data::CompositeHash

# COPYRIGHT

        Copyright (C) 2014-2016 by Ryan Gies. All rights reserved.
        Copyright (C) 2006-2013 by Livesite Networks, LLC. All rights reserved.
        Copyright (C) 2000-2005 by Ryan Gies. All rights reserved.
        Redistribution and use in source and binary forms, with or without
        modification, are permitted provided that the following conditions are met:
        * Redistributions of source code must retain the above copyright notice,
        this list of conditions and the following disclaimer.
        * The origin of this software must not be misrepresented; you must not
        claim that you wrote the original software. If you use this software in a
        product, an acknowledgment in the product documentation would be
        appreciated but is not required.
        * Altered source versions must be plainly marked as such, and must not be
        misrepresented as being the original software.
        * The name of the author may not be used to endorse or promote products
        derived from this software without specific prior written permission.

        THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED
        WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
        MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
        EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
        EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
        OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
        INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
        CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
        IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
        OF SUCH DAMAGE.
        To the best of our knowledge, no patented algorithms have been used. However, we
        do not have the resources to carry out a patent search, and therefore cannot
        give any guarantee of the above statement.

--title=Data::CompositeHash