129 lines
4.2 KiB
Perl
129 lines
4.2 KiB
Perl
use strict;
|
|
package Tie::Memoize;
|
|
use Tie::Hash;
|
|
our @ISA = 'Tie::ExtraHash';
|
|
our $VERSION = '1.1';
|
|
|
|
our $exists_token = \undef;
|
|
|
|
sub croak {require Carp; goto &Carp::croak}
|
|
|
|
# Format: [0: STORAGE, 1: EXISTS-CACHE, 2: FETCH_function;
|
|
# 3: EXISTS_function, 4: DATA, 5: EXISTS_different ]
|
|
|
|
sub FETCH {
|
|
my ($h,$key) = ($_[0][0], $_[1]);
|
|
my $res = $h->{$key};
|
|
return $res if defined $res; # Shortcut if accessible
|
|
return $res if exists $h->{$key}; # Accessible, but undef
|
|
my $cache = $_[0][1]{$key};
|
|
return if defined $cache and not $cache; # Known to not exist
|
|
my @res = $_[0][2]->($key, $_[0][4]); # Autoload
|
|
$_[0][1]{$key} = 0, return unless @res; # Cache non-existence
|
|
delete $_[0][1]{$key}; # Clear existence cache, not needed any more
|
|
$_[0][0]{$key} = $res[0]; # Store data and return
|
|
}
|
|
|
|
sub EXISTS {
|
|
my ($a,$key) = (shift, shift);
|
|
return 1 if exists $a->[0]{$key}; # Have data
|
|
my $cache = $a->[1]{$key};
|
|
return $cache if defined $cache; # Existence cache
|
|
my @res = $a->[3]($key,$a->[4]);
|
|
$a->[1]{$key} = 0, return unless @res; # Cache non-existence
|
|
# Now we know it exists
|
|
return ($a->[1]{$key} = 1) if $a->[5]; # Only existence reported
|
|
# Now know the value
|
|
$a->[0]{$key} = $res[0]; # Store data
|
|
return 1
|
|
}
|
|
|
|
sub TIEHASH {
|
|
croak 'syntax: tie %hash, \'Tie::AutoLoad\', \&fetch_subr' if @_ < 2;
|
|
croak 'syntax: tie %hash, \'Tie::AutoLoad\', \&fetch_subr, $data, \&exists_subr, \%data_cache, \%existence_cache' if @_ > 6;
|
|
push @_, undef if @_ < 3; # Data
|
|
push @_, $_[1] if @_ < 4; # exists
|
|
push @_, {} while @_ < 6; # initial value and caches
|
|
bless [ @_[4,5,1,3,2], $_[1] ne $_[3]], $_[0]
|
|
}
|
|
|
|
1;
|
|
|
|
=head1 NAME
|
|
|
|
Tie::Memoize - add data to hash when needed
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
require Tie::Memoize;
|
|
tie %hash, 'Tie::Memoize',
|
|
\&fetch, # The rest is optional
|
|
$DATA, \&exists,
|
|
{%ini_value}, {%ini_existence};
|
|
|
|
=head1 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 C<exists>) result in calls to
|
|
the functions; the modify-accesses are performed as on a normal hash.
|
|
|
|
The required arguments during C<tie> are the hash, the package, and
|
|
the reference to the C<FETCH>ing function. The optional arguments are
|
|
an arbitrary scalar $data, the reference to the C<EXISTS> function,
|
|
and initial values of the hash and of the existence cache.
|
|
|
|
Both the C<FETCH>ing function and the C<EXISTS> functions have the
|
|
same signature: the arguments are C<$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 C<EXISTS>
|
|
function is different from the C<FETCH>ing function, it should return
|
|
a TRUE value on success. The C<FETCH>ing function should return the
|
|
intended value if the key is valid.
|
|
|
|
=head1 Inheriting from B<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: $data
|
|
|
|
The rest is for internal usage of this package. In particular, if
|
|
TIEHASH is overwritten, it should call SUPER::TIEHASH.
|
|
|
|
=head1 EXAMPLE
|
|
|
|
sub slurp {
|
|
my ($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 F<fake_file1> and
|
|
F<fake_file2> fetch values $content1 and $content2, and
|
|
F<pretend_does_not_exists> will never be accessed. Additionally, the
|
|
existence of F<known_to_exist> is never checked (so if it does not
|
|
exists when its content is needed, the user of %hash may be confused).
|
|
|
|
=head1 BUGS
|
|
|
|
FIRSTKEY and NEXTKEY methods go through the keys which were already read,
|
|
not all the possible keys of the hash.
|
|
|
|
=head1 AUTHOR
|
|
|
|
Ilya Zakharevich L<mailto:perl-module-hash-memoize@ilyaz.org>.
|
|
|
|
=cut
|
|
|