NAME
PadWalker - play with other peoples' lexical variables
SYNOPSIS
...
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
. Sopeek_my(0)
returns a reference to a hash of all themy
variables that are currently in scope;peek_my(1)
returns a reference to a hash of all themy
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 theour
variables rather than themy
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 themy
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 forpeek_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 topeek_sub
, except that it only lists themy
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 useclosed_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 byvar_ref
, provided it is amy
variable used in the sub. Thesub
parameter can be either a CODE reference or a number. If it's a number, it's treated the same way as the argument topeek_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.