NAME
Tie::Memoize - add data to hash when needed
SYNOPSIS
require Tie::Memoize;
tie %hash, 'Tie::Memoize',
\&fetch, # The rest is optional
$DATA, \&exists,
{%inivalue}, {%iniexistence};
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,
{ fakefile1 => $content1, fakefile2 => $content2 },
{ pretenddoesnotexists => 0, knowntoexist => 1 };
This example treats the slightly modified contents of $directory as a
hash. The modifications are that the keys fakefile1 and fakefile2
fetch values $content1 and $content2, and pretenddoesnotexists will
never be accessed. Additionally, the existence of knowntoexist 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
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perl v5.16.3 2013-02-26 Tie::Memoize(3pm)