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.