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Tie::Memoize(3)	       Perl Programmers	Reference Guide	       Tie::Memoize(3)

       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 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

       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.

	 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).

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

       Ilya Zakharevich	<>.

perl v5.32.0			  2020-06-14		       Tie::Memoize(3)

NAME | SYNOPSIS | DESCRIPTION | Inheriting from Tie::Memoize | EXAMPLE | BUGS | AUTHOR

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