Lexical::Persistence(3)User Contributed Perl DocumentatioLnexical::Persistence(3)



NNAAMMEE
       Lexical::Persistence - Persistent lexical variable values for arbitrary
       calls.

SSYYNNOOPPSSIISS
               #!/usr/bin/perl

               use Lexical::Persistence;

               my $persistence = Lexical::Persistence->new();
               foreach my $number (qw(one two three four five)) {
                       $persistence->call(\&target, number => $number);
               }

               exit;

               sub target {
                       my $arg_number;   # Argument.
                       my $narf_x++;     # Persistent.
                       my $_i++;         # Dynamic.
                       my $j++;          # Persistent.

                       print "arg_number = $arg_number\n";
                       print "\tnarf_x = $narf_x\n";
                       print "\t_i = $_i\n";
                       print "\tj = $j\n";
               }

DDEESSCCRRIIPPTTIIOONN
       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 perists in the $lp object between _s_e_t_t_e_r_(_) and _g_e_t_t_e_r_(_).

               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 _s_e_t___c_o_n_t_e_x_t_(_) 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, _c_a_l_l_(_) 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 _w_r_a_p_(_) method will
       wrap your function in a small thunk that does the _c_a_l_l_(_) 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 _s_e_t___c_o_n_t_e_x_t_(_), are
       stored in that context.

       The _g_e_t___c_o_n_t_e_x_t_(_) 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.

       nneeww

       Create a new lexical persistence object.  This object will store one or
       more persistent contexts.  When called by this object, lexical
       variables will take on the values kept in this object.

       iinniittiiaalliizzee__ccoonntteexxttss

       This method is called by _n_e_w_(_) to declare the initial contexts for a
       new Lexical::Persistence object.  The default implementation declares
       the default "_" context.

       Override or extend it to create others as needed.

       sseett__ccoonntteexxtt NNAAMMEE,, HHAASSHH

       Store a context HASH within the persistence object, keyed on a NAME.
       Members of the context HASH are unprefixed versions of the lexicals
       they'll persist, including the sigil.  For example, this _s_e_t___c_o_n_t_e_x_t_(_)
       call declares a "request" context with predefined values for three
       variables: $request_foo, @request_foo, and %request_foo:

               $lp->set_context(
                       request => {
                               '$foo' => 'value of $request_foo',
                               '@foo' => [qw( value of @request_foo )],
                               '%foo' => { key => 'value of $request_foo{key}' }
                       }
               );

       See _p_a_r_s_e___v_a_r_i_a_b_l_e_(_) for information about how Lexical::Persistence
       decides which context a lexical belongs to and how you can change that.

       ggeett__ccoonntteexxtt NNAAMMEE

       Returns a context hash associated with a particular context name.
       Autovivifies the context if it doesn't already exist, so be careful
       there.

       ccaallll CCOODDEERREEFF,, AARRGGUUMMEENNTT__LLIISSTT

       Call CODEREF with lexical persistence and an optional ARGUMENT_LIST,
       consisting of name => value pairs.  Unlike with _s_e_t___c_o_n_t_e_x_t_(_), however,
       argument names do not need sigils.  This may change in the future,
       however, as it's easy to access an argument with the wrong variable
       type.

       The ARGUMENT_LIST is passed to the called CODEREF through @_ in the
       usual way.  They're also available as $arg_name variables for
       convenience.

       See _p_u_s_h___a_r_g___c_o_n_t_e_x_t_(_) for information about how $arg_name works, and
       what you can do to change that behavior.

       iinnvvookkee OOBBJJEECCTT,, MMEETTHHOODD,, AARRGGUUMMEENNTT__LLIISSTT

       Invoke OBJECT->METHOD(ARGUMENT_LIST) while maintaining state for the
       METHOD's lexical variables.  Written in terms of _c_a_l_l_(_), except that it
       takes OBJECT and METHOD rather than CODEREF.  See _c_a_l_l_(_) for more
       details.

       May have issues with methods invoked via AUTOLOAD, as _i_n_v_o_k_e_(_) uses
       _c_a_n_(_) to find the method's CODEREF for _c_a_l_l_(_).

       wwrraapp CCOODDEERREEFF

       Wrap a function or anonymous CODEREF so that it's transparently called
       via _c_a_l_l_(_).  Returns a coderef which can be called directly.  Named
       arguments to the call will automatically become available as $arg_name
       lexicals within the called CODEREF.

       See _c_a_l_l_(_) and _p_u_s_h___a_r_g___c_o_n_t_e_x_t_(_) for more details.

       pprreeppaarree CCOODDEE

       Wrap a CODE string in a subroutine definition, and prepend declarations
       for all the variables stored in the Lexical::Persistence default
       context.  This avoids having to declare variables explicitly in the
       code using 'my'.  Returns a new code string ready for Perl's built-in
       _e_v_a_l_(_).  From there, a program may $lp->_c_a_l_l_(_) the code or $lp->_w_r_a_p_(_)
       it.

       Also see "_c_o_m_p_i_l_e_(_)", which is a convenient wrapper for _p_r_e_p_a_r_e_(_) and
       Perl's built-in _e_v_a_l_(_).

       Also see "_d_o_(_)", which is a convenient way to _p_r_e_p_a_r_e_(_), _e_v_a_l_(_) and
       _c_a_l_l_(_) in one step.

       ccoommppiillee CCOODDEE

       _c_o_m_p_i_l_e_(_) is a convenience method to _p_r_e_p_a_r_e_(_) a CODE string, _e_v_a_l_(_)
       it, and then return the resulting coderef.  If it fails, it returns
       false, and $@ will explain why.

       ddoo CCOODDEE

       _d_o_(_) is a convenience method to _c_o_m_p_i_l_e_(_) a CODE string and execute it.
       It returns the result of CODE's execution, or it throws an exception on
       failure.

       This example prints the numbers 1 through 10.  Note, however, that _d_o_(_)
       compiles the same code each time.

               use Lexical::Persistence;

               my $lp = Lexical::Persistence->new();
               $lp->do('my $count = 0');
               $lp->do('print ++$count, "\\n"') for 1..10;

       Lexical declarations are preserved across _d_o_(_) invocations, such as
       with $count in the surrounding examples.  This behavior is part of
       _p_r_e_p_a_r_e_(_), which _d_o_(_) uses via _c_o_m_p_i_l_e_(_).

       The previous example may be rewritten in terms of _c_o_m_p_i_l_e_(_) and _c_a_l_l_(_)
       to avoid recompiling code every iteration.  Lexical declarations are
       preserved between _d_o_(_) and _c_o_m_p_i_l_e_(_) as well:

               use Lexical::Persistence;

               my $lp = Lexical::Persistence->new();
               $lp->do('my $count = 0');
               my $coderef = $lp->compile('print ++$count, "\\n"');
               $lp->call($coderef) for 1..10;

       _d_o_(_) inherits some limitations from PadWalker's _p_e_e_k___s_u_b_(_).  For
       instance, it cannot alias lexicals within _s_u_b_(_) definitions in the
       supplied CODE string.  However, Lexical::Persistence can do this with
       careful use of _e_v_a_l_(_) and some custom CODE preparation.

       ppaarrssee__vvaarriiaabbllee VVAARRIIAABBLLEE__NNAAMMEE

       This method determines whether VARIABLE_NAME should be persistent.  If
       it should, _p_a_r_s_e___v_a_r_i_a_b_l_e_(_) will return three values: the variable's
       sigil ('$', '@' or '%'), the context name in which the variable
       persists (see _s_e_t___c_o_n_t_e_x_t_(_)), and the name of the member within that
       context where the value is stored.  _p_a_r_s_e___v_a_r_i_a_b_l_e_(_) returns nothing if
       VARIABLE_NAME should not be persistent.

       _p_a_r_s_e___v_a_r_i_a_b_l_e_(_) also determines whether the member name includes its
       sigil.  By default, the "arg" context is the only one with members that
       have no sigils.  This is done to support the unadorned argument names
       used by _c_a_l_l_(_).

       This method implements a default behavior.  It's intended to be
       overridden or extended by subclasses.

       ggeett__mmeemmbbeerr__rreeff SSIIGGIILL,, CCOONNTTEEXXTT,, MMEEMMBBEERR

       This method fetches a reference to the named MEMBER of a particular
       named CONTEXT.  The returned value type will be governed by the given
       SIGIL.

       Scalar values are stored internally as scalars to be consistent with
       how most people store scalars.

       The persistent value is created if it doesn't exist.  The initial value
       is undef or empty, depending on its type.

       This method implements a default behavior.  It's intended to be
       overridden or extended by subclasses.

       ppuusshh__aarrgg__ccoonntteexxtt AARRGGUUMMEENNTT__LLIISSTT

       Convert a named ARGUMENT_LIST into members of an argument context, and
       call _s_e_t___c_o_n_t_e_x_t_(_) to declare that context.  This is how $arg_foo
       variables are supported.  This method returns the previous context,
       fetched by _g_e_t___c_o_n_t_e_x_t_(_) before the new context is set.

       This method implements a default behavior.  It's intended to be
       overridden or extended by subclasses.  For example, to redefine the
       parameters as $param_foo.

       See _p_o_p___a_r_g___c_o_n_t_e_x_t_(_) for the other side of this coin.

       ppoopp__aarrgg__ccoonntteexxtt OOLLDD__AARRGG__CCOONNTTEEXXTT

       Restores OLD_ARG_CONTEXT after a target function has returned.  The
       OLD_ARG_CONTEXT is the return value from the _p_u_s_h___a_r_g___c_o_n_t_e_x_t_(_) call
       just prior to the target function's call.

       This method implements a default behavior.  It's intended to be
       overridden or extended by subclasses.

SSEEEE AALLSSOO
       POE::Stage, Devel::LexAlias, PadWalker, Catalyst::Controller::BindLex.

       BBUUGG TTRRAACCKKEERR

       https://rt.cpan.org/Dist/Display.html?Status=Active&Queue=Lexical-Persistence

       RREEPPOOSSIITTOORRYY

       http://thirdlobe.com/svn/lex-per/

       OOTTHHEERR RREESSOOUURRCCEESS

       http://search.cpan.org/dist/Lexical-Persistence/

CCOOPPYYRRIIGGHHTT
       Lexical::Persistence in copyright 2006-2009 by Rocco Caputo.  All
       rights reserved.  Lexical::Persistence is free software.  It is
       released under the same terms as Perl itself.

AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS
       Thanks to Matt Trout and Yuval Kogman for lots of inspiration.  They
       were the demon and the other demon sitting on my shoulders.

       Nick Perez convinced me to make this a class rather than persist with
       the original, functional design.  While Higher Order Perl is fun for
       development, I have to say the move to OO was a good one.

       Paul "LeoNerd" Evans contributed the _c_o_m_p_i_l_e_(_) and _e_v_a_l_(_) methods.

       The South Florida Perl Mongers, especially Jeff Bisbee and Marlon
       Bailey, for documentation feedback.

       irc://irc.perl.org/poe for support and feedback.



perl v5.10.0                      2009-07-27           Lexical::Persistence(3)