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Re: Caller's Variables

by Abigail-II (Bishop)
on Jul 08, 2002 at 12:29 UTC ( [id://180149]=note: print w/replies, xml ) Need Help??


in reply to Caller's Variables

There are two types of variables you can modify in your callers namespace:
  • All package variables (well, technically, package variables are the only variables with a "namespace").
  • All lexical variables that share the same scope as your subroutine.
That is, lexical variables that don't share a scope are unreachable. And that's a good thing, that's why you have lexical variables in the first place.

Abigail

Replies are listed 'Best First'.
Re: Re: Caller's Variables
by broquaint (Abbot) on Jul 08, 2002 at 13:30 UTC
    That is, lexical variables that don't share a scope are unreachable.
    Not strictly true since you can modify lexical variables with the help of PadWalker. Here's some code from the docs
    sub increment_my_x { my $h = peek_my (1); ${$h->{'$x'}}++; } my $x=5; increment_my_x; print $x; # prints 6
    Although you'd have to be quite a disturbed individual to use this sort of thing in production any code ;-)
    HTH

    _________
    broquaint

      I could see one or two valid uses. The one place I've used it for production was a tied hash package. We wanted to be able to alias package vars in the hash values with vars from the caller. Retrofitting this to older code was a pain as they HAD to be package variables so we changed the alias sub to look at caller's lexicals and then the package vars.

      -Lee

      "To be civilized is to deny one's nature."
      Update
      While on the subject, I should mention a bug/feature of PadWalker. It will NOT see all lexicals visable where the subroutine is called if you have a bare block
      #!/usr/bin/perl -w use strict; use PadWalker qw(peek_my); my ($oa,$ob) = ("Outer One", "Outer Two"); { my $inb = "Bare Block"; # Will not be seen by peek_my peeper(); } sub peeper { my $c = peek_my(1); print "Lexicals:\n", (map { "Found $_ with value $c->{$_}\n" } sor +t keys %$c ),"\n"; }


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