Tie::Memoize - add data to hash when needed
require Tie::Memoize;
tie %hash, 'Tie::Memoize',
\&fetch, # The rest is optional
$DATA, \&exists,
{%ini_value}, {%ini_existence};
Perl Programmers Reference Guide Tie::Memoize(3)
NAME
Tie::Memoize - add data to hash when needed
SYNOPSIS
require Tie::Memoize;
tie %hash, 'Tie::Memoize',
\&fetch, # The rest is optional
$DATA, \&exists,
{%ini_value}, {%ini_existence};
DESCRIPTION
This package allows a tied hash to autoload its values on the first
access, and to use the cached value on the following accesses.
Only read-accesses (via fetching the value or "exists") result in calls
to the functions; the modify-accesses are performed as on a normal
hash.
The required arguments during "tie" are the hash, the package, and the
reference to the "FETCH"ing function. The optional arguments are an
arbitrary scalar $data, the reference to the "EXISTS" function, and
initial values of the hash and of the existence cache.
Both the "FETCH"ing function and the "EXISTS" functions have the same
signature: the arguments are "$key, $data"; $data is the same value as
given as argument during tie()ing. Both functions should return an
empty list if the value does not exist. If "EXISTS" function is
different from the "FETCH"ing function, it should return a TRUE value
on success. The "FETCH"ing function should return the intended value
if the key is valid.
Inheriting from Tie::Memoize
The structure of the tied() data is an array reference with elements
0: cache of known values
1: cache of known existence of keys
2: FETCH function
3: EXISTS function
4: $data
The rest is for internal usage of this package. In particular, if
TIEHASH is overwritten, it should call SUPER::TIEHASH.
EXAMPLE
sub slurp {
my ($key, $dir) = shift;
open my $h, '<', "$dir/$key" or return;
local $/; <$h> # slurp it all
}
sub exists { my ($key, $dir) = shift; return -f "$dir/$key" }
tie %hash, 'Tie::Memoize', \&slurp, $directory, \&exists,
{ fake_file1 => $content1, fake_file2 => $content2 },
{ pretend_does_not_exists => 0, known_to_exist => 1 };
This example treats the slightly modified contents of $directory as a
hash. The modifications are that the keys fake_file1 and fake_file2
fetch values $content1 and $content2, and pretend_does_not_exists will
never be accessed. Additionally, the existence of known_to_exist is
never checked (so if it does not exists when its content is needed, the
user of %hash may be confused).
BUGS
FIRSTKEY and NEXTKEY methods go through the keys which were already
read, not all the possible keys of the hash.
AUTHOR
Ilya Zakharevich <mailto:perl-module-hash-memoize@ilyaz.org>.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+-----------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------------+
|Availability | runtime/perl-532 |
+---------------+-----------------------+
|Stability | Pass-through volatile |
+---------------+-----------------------+
NOTES
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from
http://www.cpan.org/src/5.0/perl-5.32.0.tar.gz.
Further information about this software can be found on the open source
community website at https://www.perl.org/.
perl v5.32.0 2020-06-14 Tie::Memoize(3)