PadWalker - play with other peoples' lexical variables
use PadWalker qw(peek_my peek_our peek_sub closed_over);
...
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 the Data::Dump::Streamer manpage, 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
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.
Devel::LexAlias, Devel::Caller, Sub::Parameters
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.
|