=head1 NAME

Data::CompositeHash - 

=head1 SYNOPSIS



=head1 EXPORTS

Nothing exported by default

=over



=back

=head1 DEPENDENCIES

This module requires these other modules and libraries:

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

=head1 DESCRIPTION



=head1 EXAMPLES

This example will B<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 B<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;



I<will return>:

  a1b2c3


This example will B<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;



I<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;



I<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};



I<will return>:

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



=head1 PUBLIC INTERFACE

=head2 new

=over

=item Create a new CompositeHash





This example will B<not> abort:


  use Data::CompositeHash;



This example will abort:

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




=back


=head2 shift

=over

=item Shift a hash from the composite stack





This example will B<not> return a defined value:


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




=back


=head2 unshift

=over

=item 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};



I<will return>:

  a1



=back


=head2 push

=over

=item 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};



I<will return>:

  a2



=back


=head2 pop

=over

=item Pop a hash off the composite stack





This example will B<not> return a defined value:


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




=back




=head1 AUTHORS

    Ryan Gies <ryangies@cpan.org>

=head1 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.

=cut

