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PadWalker v2.5 - Robin Houston

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 usu-
   ally 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 dep-
   recated in a future version in favour of some alternative inter-
   face.

   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 Father Chrysostomous, Richard Soberberg, Florian Ragwitz,
   Yuval Kogman, and Fuji, Goro, bug-spotting from Peter Scott and Dave Mitchell, and
   suggestions from demerphq.

SEE ALSO Devel::LexAlias, Devel::Caller, Sub::Parameters

COPYRIGHT Copyright (c) 2000-2012, Robin Houston. All Rights Reserved. This mod- ule is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.