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ex::override - Perl pragma to override core functions


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

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

  no ex::override 'ucfirst';

  ucfirst( 'MAKE THIS RIGHT' );


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

Overriding a function

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

Overriding a core function happens at compile time. Arguments are passed to "ex::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 ex::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 ex::override length => sub { length join '', @_ };

Overriding a function globaly

Don't do this without a very good reason!

"ex::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 ex::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 ex::override; # remove _all_ overrides

  no ex::override 'values';

  no ex::override 'GLOABL_length';


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.


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


Casey West, <>


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