/ 
override-1.01
/ override

NAME

override - Perl pragma to override core functions

SYNOPSIS

use override ucfirst => sub {
                             # make sure only the first
                             # letter is uppercased
                             ucfirst( lc( shift ) );
                            };

ucfirst( 'MAKE THIS RIGHT' );
# Make this right

no override 'ucfirst';

ucfirst( 'MAKE THIS RIGHT' );
# MAKE THIS RIGHT

DESCRIPTION

"override" is an easy way to override core perl functions.

Overriding a function

use override
  length => \&mylength,
  open   => \&myopen;

Overriding a core function happens at compile time. Arguments are passed to "override" in a name based, or hash style. The key is the name of the core function to override, the value is your subroutine to replace the core's.

Using an overriden funtion

Nothing changes on the surface. If you override "stat", then you still use "stat" the same way.

NOTE: This is only true if you are keeping the same prototype as the function you've overriden. To do this, you must define your prototype:

use override values => sub (\%) { values %{+shift} };

If you don't use this same prototype or force yourself to use the function the same, you can extend the functionality of a core function:

# length of all arguments passed to length()
use override length => sub { length join '', @_ };

Overriding a function globaly

Don't do this without a very good reason!

"override" allows you the ability to override core functions globaly. Any packages that inherit from yours will use your function override. There are good reasons for doing this, if you think you need to, make sure you have a good reason.

use override
  GLOBAL_length => sub {
                        # prevent someone from passing a list
                        croak "Don't do that!" if @_ > 1;
                        length shift
                       };

NOTE: If you globaly override a function in a package, only that package can remove it.

Removing your override

This works the same way that "no strict" works.

no override; # remove _all_ overrides

no override 'values';

no override 'GLOABL_length';

TIPS

Get a list of overrideable function

If you have the Perl source laying around, go to it's root dir and try this:

perl -lne 'print /_(\w+)/ if /return -K/' toke.c

You'll have to weed out which ones are functions ( vs. operators, etc. ).

Get a functions prototype
perl -lwe 'print prototype "CORE::length"'

This prints the prototype, or "Use of uninitialized variable..." if there isn't one.

TODO

Find a way to preserve prototypes so the user doesn't have to know them.

AUTHOR

Casey R. Tweten, crt@kiski.net

COPYRIGHT

Copyright (c) 2000 Casey R. Tweten <crt@kiski.net>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.