Sub::AliasedUnderscore - transform a subroutine that operates on $_ into one that operates on $_[0]


   use Sub::AliasedUnderscore qw/transform transformed/;

   my $increment = sub { $_++ };
   $increment = transform $increment;

   $_ = 1; 

   my $a = 41;
   $increment->($a); # returns 41
   # $a is now 42; $_ is still 1

   my $decrement = transformed { $_-- };
   # $a is now 41; $_ is still 1


Often you'll want to accept a subroutine that operates on $_, like map and grep do. The details of getting $_ to work that way are inconvenient to worry about every time, so this module abstracts that away. Transform the subroutine that touches $_ with transform, and then treat it as though it is operating on $_[0].


Nothing by default. If you want transform or transformed, request them in the import list.



Transforms $sub to modify $_[0] instead of $_.

This means you can write your subroutine as though it were the first argument of map or grep, but execute it like $sub-($arg)>.

Everything works exactly the same as map or grep -- $_ is localized, but aliased to whatever you call the subroutine with. That means that modifying $_ in $sub will modify the argument passed to the transformed sub, but won't touch the $_ that already exists.

It makes $_ DWIM.

transformed BLOCK

Like transform, but accepts a code block instead of a coderef:

  my $sub = transformed { do something to $_ }
  $sub->($a); # $a is $_ in the above block


None known; report to RT.


The repository is managed by git. You can clone the repository with:

   git clone git://

Patches welcome!


Jonathan Rockway


Copyright (c) 2007 Jonathan Rockway. You may use, modify, and distribute this code under the same conditions as Perl itself.