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Manual Reference Pages  -  GENEZZO::PUSHHASH::HPH (3)

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NAME

Genezzo::PushHash::hph.pm - an impure virtual class module that defines a *hierarchical* "push hash", a hash that generates its own unique key for each value. Values are "pushed" into the hash, similar to pushing into an array. Hierarchical pushhashes must be supplied with a factory method which manufactures additional pushhashes as necessary.

CONTENTS

SYNOPSIS



 use Genezzo::PushHash::hph;

 sub make_fac {
    my $tclass = shift;
    my %args = (
                @_);

    my %td_hash1  = ();

    my $newfunc =
        sub {
            my $tiehash1 =
                tie %td_hash1, $tclass, %args;

            return $tiehash1;
        };
    return $newfunc;
 }

 my $fac1 = make_fac(Genezzo::PushHash::PHFixed);

 %args =
    (
     factory  => $fac1
    );

 my %tied_hash = ();

 my $tie_val =
    tie %tied_hash, Genezzo::PushHash::hph, %args;

 my $newkey = $tie_val->HPush("this is a test");

 $tied_hash{$newkey} = "update this entry";

 my $getcount = $tie_val->HCount();



DESCRIPTION

A hierarchical pushhash (hph) is a pushhash built upon a collection of other pushhashes. A push into the top-level hash is routed into one of the bottom hashes. If the bottom hashes are full (push fails), the top-level pushhash uses the factory method to create or obtain a new pushhash.

The hph uses a split-level identifier scheme to route STOREs and FETCHes to the appropriate bottom level hashes. For example, the top-level hash might have three children identified with integer prefixes 1, 2, and 3. Pushes into hash 1 would return keys 1/1, 1/2, 1/3, etc. until it fills up, at which point the top-level hash would redirect pushes into hash 2, generating keys 2/1, 2/2, 2/3, etc. When key 1/2 is fetched, the top-level hash splits the key and directs child hash 1 to fetch key 2. Iteration over keys is similar: the parent interates over the set of child hashes, and each child iterates over its set of keys.

You may construct hierarchical pushhashes of arbitrary depth.

    EXPORT

RIDSEP — (Row) Identifier Separator character - ‘‘/’’ by default.
RIDSEPRX — Regular Expression for RIDSEP - used to handle case of ‘‘.’’ as separator, or other regexp metachars, for internal RID join and split operations.
MAXCOUNT — no max if -1, else maximum number of elements for this hash

CONCEPTS and INTERNALS - useful for implementors

A hph is constructed of N pushhash chunks, and the elements of each chunk are referred to as slices. Typically, one chunk is current — we push into the current chunk until it fills up, at which point the hph attempts to make a new one. Key identifiers are called rids, and a rid may have multiple parts, e.g. 1/2/3/4. When this rid is split, the first part, 1, is the chunk number, and the remainder 2/3/4 is the slice number. The basic implementation uses positive integers for chunk and slice numbers — zeroes reset the FIRSTKEY/NEXTKEY mechanism and may indicate errors, among other things.

The following methods are <B>privateB> to hph and should only be used in the construction of subclasses and friend classes.
_currchunkno get the number of the current (active) chunk. NOTE WELL: when constructing push hash classes, remember that current has the specific meaning of the insert high-water mark — the current insertion point. It’s not necessarily the last chunk that you were using, or the chunk that is currently cached.
_get_current_chunk return the current chunk
_make_new_chunk construct a new chunk and return it
_get_a_chunk given a chunk number, returns the chunk
_get_chunk_and_slice given a rid, it returns the actual chunk (not the chunk number) and the slice number.
_joinrid/_splitrid construct and deconstruct rid’s from/to the chunknumber and the slice number using the rid separator regular expression.
_First_Chunkno/_Next_Chunkno methods to iterate over the chunk numbers.

AUTHOR

Jeffrey I. Cohen, jcohen@genezzo.com

SEE ALSO

Genezzo::PushHash::PushHash, perl(1).

Copyright (c) 2003, 2004, 2005, 2006 Jeffrey I Cohen. All rights reserved.



    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA



Address bug reports and comments to: jcohen@genezzo.com

For more information, please visit the Genezzo homepage at <http://www.genezzo.com>

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perl v5.20.3 GENEZZO::PUSHHASH::HPH (3) 2006-10-20

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