NAME

       PadWalker - play with other peoples' lexical variables

SYNOPSIS

         use PadWalker qw(peek_my peek_our peek_sub closed_over);
         ...

DESCRIPTION

       PadWalker is a module which allows you to inspect (and even change!)  lexical variables in
       any subroutine which called you. It will only show those variables which are in scope at
       the point of the call.

       PadWalker is particularly useful for debugging. It's even used by Perl's built-in
       debugger. (It can also be used for evil, of course.)

       I wouldn't recommend using PadWalker directly in production code, but it's your call. Some
       of the modules that use PadWalker internally are certainly safe for and useful in
       production.

       peek_my LEVEL
       peek_our LEVEL
           The LEVEL argument is interpreted just like the argument to "caller".  So peek_my(0)
           returns a reference to a hash of all the "my" variables that are currently in scope;
           peek_my(1) returns a reference to a hash of all the "my" variables that are in scope
           at the point where the current sub was called, and so on.

           "peek_our" works in the same way, except that it lists the "our" variables rather than
           the "my" variables.

           The hash associates each variable name with a reference to its value. The variable
           names include the sigil, so the variable $x is represented by the string '$x'.

           For example:

             my $x = 12;
             my $h = peek_my (0);
             ${$h->{'$x'}}++;

             print $x;  # prints 13

           Or a more complex example:

             sub increment_my_x {
               my $h = peek_my (1);
               ${$h->{'$x'}}++;
             }

             my $x=5;
             increment_my_x;
             print $x;  # prints 6

       peek_sub SUB
           The "peek_sub" routine takes a coderef as its argument, and returns a hash of the "my"
           variables used in that sub. The values will usually be undefined unless the sub is in
           use (i.e. in the call-chain) at the time. On the other hand:

             my $x = "Hello!";
             my $r = peek_sub(sub {$x})->{'$x'};
             print "$$r\n";        # prints 'Hello!'

           If the sub defines several "my" variables with the same name, you'll get the last one.
           I don't know of any use for "peek_sub" that isn't broken as a result of this, and it
           will probably be deprecated in a future version in favour of some alternative
           interface.

       closed_over SUB
           "closed_over" is similar to "peek_sub", except that it only lists the "my" variables
           which are used in the subroutine but defined outside: in other words, the variables
           which it closes over. This does have reasonable uses: see Data::Dump::Streamer, for
           example (a future version of which may in fact use "closed_over").

       set_closed_over SUB, HASH_REF
           "set_closed_over" reassigns the pad variables that are closed over by the subroutine.

           The second argument is a hash of references, much like the one returned from
           "closed_over".

       var_name LEVEL, VAR_REF
       var_name SUB,   VAR_REF
           "var_name(sub, var_ref)" returns the name of the variable referred to by "var_ref",
           provided it is a "my" variable used in the sub. The "sub" parameter can be either a
           CODE reference or a number. If it's a number, it's treated the same way as the
           argument to "peek_my".

           For example,

             my $foo;
             print var_name(0, \$foo);    # prints '$foo'

             sub my_name {
               return var_name(1, shift);
             }
             print my_name(\$foo);        # ditto

AUTHOR

       Robin Houston <robin@cpan.org>

       With contributions from Richard Soberberg, Jesse Luehrs and Yuval Kogman, bug-spotting
       from Peter Scott, Dave Mitchell and Goro Fuji, and suggestions from demerphq.

SEE ALSO

       Devel::LexAlias, Devel::Caller, Sub::Parameters

COPYRIGHT

       Copyright (c) 2000-2009, Robin Houston. All Rights Reserved.  This module is free
       software. It may be used, redistributed and/or modified under the same terms as Perl
       itself.