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

       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};

       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


perl v5.8.5                 2002-11-06                          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 $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).

       FIRSTKEY and NEXTKEY methods go through the keys which
       were already read, not all the possible keys of the hash.

       Ilya Zakharevich <mailto:perl-module-hash-memo-

perl v5.8.5                 2002-11-06                          2