Jeffrey Cohen
and 1 contributors

NAME - 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.


 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();


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.


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 private to hph and should only be used in the construction of subclasses and friend classes.


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.


return the current chunk


construct a new chunk and return it


given a chunk number, returns the chunk


given a rid, it returns the actual chunk (not the chunk number) and the slice number.


construct and deconstruct rid's from/to the chunknumber and the slice number using the rid separator regular expression.


methods to iterate over the chunk numbers.


Jeffrey I. Cohen,


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
    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

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