NAME

Lexical::Alias - makes a lexical an alias for another variable

SYNOPSIS

  use 5.008;
  use Lexical::Alias;

  my ($src, $dst);
  alias $src, $dst;

  my (@src, @dst);
  alias @src, @dst;

  my (%src, %dst);
  alias %src, %dst;

  # modifying $src/@src/%src
  # modifies $dst/@dst/%dst,
  # and vice-versa

  # or, if supporting Perls prior to v5.8:

  use Lexical::Alias qw( alias_r alias_s alias_a alias_h );

  my ($src, $dst);
  alias_s $src, $dst;

  my (@src, @dst);
  alias_a @src, @dst;

  my (%src, %dst);
  alias_h %src, %dst;

  alias_r \$src, \$dst;
  alias_r \@src, \@dst;
  alias_r \%src, \%dst;

  # if you prefer the alias come first...
  $Lexical::Alias::SWAP = 1;
  alias $dst, $src;  # $dst is an alias for $src

DESCRIPTION

This module allows you to alias a lexical (declared with "my") variable to another variable (package or lexical). You will receive a fatal error if you try aliasing a scalar to something that is not a scalar (etc.).

Parameter Swaping (new!)

Version 0.04 introduced the $Lexical::Alias::SWAP variable. When it is true, the arguments to the aliasing functions are expected in reverse order; that is, the alias comes first, and the source variable second.

(Thanks to Jenda from perlmonks.org for requesting this.)

Exported Functions

"alias(src, dst)"
Makes dst (which must be lexical) an alias to src (which can be either lexical or a package variable). src and dst must be the same data type (scalar and scalar, array and array, hash and hash).

This is only available in Perl v5.8 and later, where it is exported automatically.
"alias_s($src, $dst)"
Makes dst (which must be lexical) an alias to src (which can be either lexical or a package variable). This is not exported by default.
"alias_a(@src, @dst)"
Makes dst (which must be lexical) an alias to src (which can be either lexical or a package variable). This is not exported by default.
"alias_h(%src, %dst)"
Makes dst (which must be lexical) an alias to src (which can be either lexical or a package variable). This is not exported by default.
"alias_r(\src, \dst)"
Makes dst (which must be lexical) an alias to src (which can be either lexical or a package variable). src and dst must be the same data type (scalar and scalar, array and array, hash and hash). This is not exported by default.

Caveats

If you alias one lexical to another lexical, then making another alias to either lexical makes all three lexicals point to the same data.

  use Lexical::Alias;

  my ($x, $y, $z);
  alias $x => $y;  # $y is an alias for $x
  alias $z => $y;  # $y (and thus $x) is an alias for $z
  $z = 10;
  print $x;        # 10

This is not a bug.

However, there does appear to be a bug in Perl 5.8.0 (which has been fixed in the development version 5.9.0); when these functions are used in a subroutine, they appear to not work fully:

  my $orig = 1;
  my $alias = 99;
  alias $orig => $alias;
  print "$orig = $alias\n";

  sub foo {
    my $orig = 1;
    my $alias = 99;
    alias $orig => $alias;
    print "foo(): $orig = $alias\n";
  }

  foo();

The expected output is "1 = 1" and "foo(): 1 = 1". It is not so. The second output is "foo(): 1 = 99". Jenda pointed this out to me, and I do not know where in the source the bug is, but it will be fixed for the next release of Perl (5.8.1).

AUTHOR

Jeff "japhy" Pinyan, japhy@pobox.com

Thanks to Tye McQueen for a bug fix -- this module should work from 5.005 on.

http://www.pobox.com/~japhy/