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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 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,
	{ 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>.

Index for Section 3

Alphabetical listing for T

Top of page