


Tie::Memoize(3p) Perl Programmers Reference GuideTie::Memoize(3p)


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








perl v5.10.1                2008-09-29                          1





Tie::Memoize(3p) Perl Programmers Reference GuideTie::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
       $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>.































perl v5.10.1                2008-09-29                          2


