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# no good because Attribute::Handlers doesn't run at the right phase in a
# require or eval
# Copyright 2008, 2009, 2010 Kevin Ryde
# This file is part of constant-defer.
#
# constant-defer is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 3, or (at your option) any later
# version.
#
# constant-defer is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with constant-defer. If not, see <http://www.gnu.org/licenses/>.
package Attribute::MemoizeToConstant;
use Attribute::Handlers;
## no critic (RequireUseStrict RequireUseWarnings)
no strict;
no warnings;
push @UNIVERSAL::ISA, __PACKAGE__;
use constant DEBUG => 0;
our $c;
my @pending;
my $checked = 0;
sub MODIFY_CODE_ATTRIBUTES {
my ($package, $coderef, @attrs) = @_;
if (DEBUG) { print "MemoizeToConstant pending $package $coderef\n"; }
push @pending, [$package, $coderef];
if ($checked) {
run_pending();
}
return grep {$_ ne 'MemoizeToConstant'} @attrs;
}
CHECK {
if (DEBUG) { print "MemoizeToConstant CHECK\n"; }
$checked = 1;
run_pending();
}
sub run_pending {
while (@pending) {
my ($package, $oldcode) = @{pop @pending};
if (DEBUG) { print " $package $oldcode\n"; }
$c = $oldcode;
require Scalar::Util;
Scalar::Util::weaken ($c);
my $found;
my $phash = \%{"${package}::"};
foreach my $name (keys %$phash) {
my $glob = $phash->{$name};
ref(\$glob) eq 'GLOB' or next;
(*{$glob}{CODE} || 0) == $oldcode or next;
my $fullname = "${package}::$name";
if (DEBUG) { print " install to $fullname\n"; }
*$fullname = sub () {
my $value = $oldcode->(@_);
*$fullname = sub () { $value };
return $value;
};
$found = 1;
}
$found or warn "MemoizeToConstant func $oldcode not found in $package";
}
}
1;
__END__
# sub make_func {
# return sub () {
# my $value = $_[0]oldcode->(@_);
# *$sym = sub () { $value };
# return $value;
# }
# }
# use Data::Dumper;
# print Dumper(\@_);
#
# use Data::Dump;
# print Data::Dump::dump(\*main::foo);
#
# my $x = findsym ($package, $coderef);
# print "findsym ",Dumper($x);
#
# no strict;
#
# my $type = ref($coderef);
# Attribute::Handlers holds onto to the original coderef, so it's not freed
# when the func is turned into a constant ...
package Attribute::MemoizeToConstant;
use Attribute::Handlers;
use strict;
use warnings;
our $VERSION = 1;
use constant DEBUG => 0;
our $c;
sub UNIVERSAL::MemoizeToConstant : ATTR(CODE) {
my ($package, $typeglob, $oldcode) = @_;
$c = $oldcode;
Scalar::Util::weaken ($c);
if (DEBUG) {
print "MemoizeToConstant on '$package' '",
*{$typeglob}{NAME}, "' ", $oldcode,"\n";
}
no warnings;
*$typeglob = sub () {
my $value = $oldcode->(@_);
*$typeglob = sub () { $value };
return $value;
};
}
1;
__END__
=head1 NAME
Attribute::MemoizeToConstant -- memoize functions to become constants
=head1 SYNOPSIS
use Attribute::MemoizeToConstant;
sub myfunc : MemoizeToConstant {
# some long calculation
return $x;
}
=head1 BUGS!
Doesn't work when used in a module or file which is loaded by C<require>,
C<do>, etc, only from the main program and things brought in C<use>.
=head1 DESCRIPTION
Attribute C<MemoizeToConstant> arranges for a function to be memoized so its
first call runs the code but it's then transformed into a constant sub (like
C<use constant>) with that first return value.
=head1 SEE ALSO
=for comment
Actually it wants to be attributes(3perl) to avoid attributes(3ncurses), but
the formatters complain about that ...
L<Attribute::Memoize>, L<Memoize::Attrs>, L<attributes>,
L<Attribute::Handlers>, L<Memoize>
=cut
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