perl-Lexical-Persistence

Lexical::Persistence does a few things, all related. Note that all the
behaviors listed here are the defaults. Subclasses can override nearly
every aspect of Lexical::Persistence's behavior.
Lexical::Persistence lets your code access persistent data through lexical
variables. This example prints "some value" because the value of $x
persists in the $lp object between setter() and getter().
use Lexical::Persistence;

my $lp = Lexical::Persistence->new();
$lp->call(\&setter);
$lp->call(\&getter);

sub setter { my $x = "some value" }
sub getter { print my $x, "\n" }


Lexicals with leading underscores are not persistent.
By default, Lexical::Persistence supports accessing data from multiple
sources through the use of variable prefixes. The set_context() member sets
each data source. It takes a prefix name and a hash of key/value pairs. By
default, the keys must have sigils representing their variable types.
use Lexical::Persistence;

my $lp = Lexical::Persistence->new();
$lp->set_context( pi => { '$member' => 3.141 } );
$lp->set_context( e => { '@member' => [ 2, '.', 7, 1, 8 ] } );
$lp->set_context(
	animal => {
		'%member' => { cat => "meow", dog => "woof" }
	}
);

$lp->call(\&display);

sub display {
	my ($pi_member, @e_member, %animal_member);

	print "pi = $pi_member\n";
	print "e = @e_member\n";
	while (my ($animal, $sound) = each %animal_member) {
		print "The $animal goes... $sound!\n";
	}
}


And the corresponding output:
pi = 3.141
e = 2 . 7 1 8
The cat goes... meow!
The dog goes... woof!


By default, call() takes a single subroutine reference and an optional list
of named arguments. The arguments will be passed directly to the called
subroutine, but Lexical::Persistence also makes the values available from
the "arg" prefix.
use Lexical::Persistence;

my %animals = (
	snake => "hiss",
	plane => "I'm Cartesian",
);

my $lp = Lexical::Persistence->new();
while (my ($animal, $sound) = each %animals) {
	$lp->call(\&display, animal => $animal, sound => $sound);
}

sub display {
	my ($arg_animal, $arg_sound);
	print "The $arg_animal goes... $arg_sound!\n";
}


And the corresponding output:
The plane goes... I'm Cartesian!
The snake goes... hiss!


Sometimes you want to call functions normally. The wrap() method will wrap
your function in a small thunk that does the call() for you, returning a
coderef.
use Lexical::Persistence;

my $lp = Lexical::Persistence->new();
my $thunk = $lp->wrap(\&display);

$thunk->(animal => "squirrel", sound => "nuts");

sub display {
	my ($arg_animal, $arg_sound);
	print "The $arg_animal goes... $arg_sound!\n";
}


And the corresponding output:
The squirrel goes... nuts!


Prefixes are the characters leading up to the first underscore in a lexical
variable's name. However, there's also a default context named underscore.
It's literally "_" because the underscore is not legal in a context name by
default. Variables without prefixes, or with prefixes that have not been
previously defined by set_context(), are stored in that context.
The get_context() member returns a hash for a named context. This allows
your code to manipulate the values within a persistent context.
use Lexical::Persistence;

my $lp = Lexical::Persistence->new();
$lp->set_context(
	_ => {
		'@mind' => [qw(My mind is going. I can feel it.)]
	}
);

while (1) {
	$lp->call(\&display);
	my $mind = $lp->get_context("_")->{'@mind'};
	splice @$mind, rand(@$mind), 1;
	last unless @$mind;
}

sub display {
	my @mind;
	print "@mind\n";
}


Displays something like:
My mind is going. I can feel it.
My is going. I can feel it.
My is going. I feel it.
My going. I feel it.
My going. I feel
My I feel
My I
My


It's possible to create multiple Lexical::Persistence objects, each with a
unique state.
use Lexical::Persistence;

my $lp_1 = Lexical::Persistence->new();
$lp_1->set_context( _ => { '$foo' => "context 1's foo" } );

my $lp_2 = Lexical::Persistence->new();
$lp_2->set_context( _ => { '$foo' => "the foo in context 2" } );

$lp_1->call(\&display);
$lp_2->call(\&display);

sub display {
	print my $foo, "\n";
}


Gets you this output:
context 1's foo
the foo in context 2


You can also compile and execute perl code contained in plain strings in a
a lexical environment that already contains the persisted variables.
use Lexical::Persistence;

my $lp = Lexical::Persistence->new();

$lp->do( 'my $message = "Hello, world" );

$lp->do( 'print "$message\n"' );


Which gives the output:
Hello, world


If you come up with other fun uses, let us know.

          

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License: Artistic-1.0 or GPL-1.0+
URL: http://search.cpan.org/dist/Lexical-Persistence/