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 fol
lowing 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 differ
ent 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: $data - The rest is for internal usage of this package. In par
ticular, if TIEHASH is overwritten, it should call
SUPER::TIEHASH.
EXAMPLE
- sub slurp {
- my ($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 $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-memo
ize@ilyaz.org>.