Tie::Memoize(3p)Perl Programmers Reference Guide Tie::Memoize(3p)NAMETie::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 follow-
ing 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 pack-
age, and the reference to the "FETCH"ing function. The
optional arguments are an arbitrary scalar $data, the refer-
ence to the "EXISTS" function, and initial values of the
hash and of the existence cache.
Both the "FETCH"ing function and the "EXISTS" functions have
the same signature: the arguments are "$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 suc-
cess. 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: $data
The rest is for internal usage of this package. In particu-
lar, if TIEHASH is overwritten, it should call
SUPER::TIEHASH.
EXAMPLEperl v5.8.8 2005-02-05 1
Tie::Memoize(3p)Perl Programmers Reference Guide Tie::Memoize(3p)
sub slurp {
my ($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 $con-
tent2, 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>.
perl v5.8.8 2005-02-05 2
