perlfunc: re-document old split() @_ side effect

[perl5.git] / lib / CORE.pod

=head1 NAME

CORE - Namespace for Perl's core routines

=head1 SYNOPSIS

    BEGIN {
        *CORE::GLOBAL::hex = sub { 1; };
    }

    print hex("0x50"),"\n";			# prints 1
    print CORE::hex("0x50"),"\n";		# prints 80
    CORE::say "yes";				# prints yes

    BEGIN { *shove = \&CORE::push; }
    shove @array, 1,2,3;			# pushes on to @array

=head1 DESCRIPTION

The C<CORE> namespace gives access to the original built-in functions of
Perl.  The C<CORE> package is built into
Perl, and therefore you do not need to use or
require a hypothetical "CORE" module prior to accessing routines in this
namespace.

A list of the built-in functions in Perl can be found in L<perlfunc>.

For all Perl keywords, a C<CORE::> prefix will force the built-in function
to be used, even if it has been overridden or would normally require the
L<feature> pragma.  Despite appearances, this has nothing to do with the
CORE package, but is part of Perl's syntax.

For many Perl functions, the CORE package contains real subroutines.  This
feature is new in Perl 5.16.  You can take references to these and make
aliases.  However, some can only be called as barewords; i.e., you cannot
use ampersand syntax (C<&foo>) or call them through references.  See the
C<shove> example above.  These subroutines exist for all keywords except the following:

C<__DATA__>, C<__END__>, C<and>, C<cmp>, C<default>, C<do>, C<dump>,
C<else>, C<elsif>, C<eq>, C<eval>, C<for>, C<foreach>, C<format>, C<ge>,
C<given>, C<goto>, C<grep>, C<gt>, C<if>, C<last>, C<le>, C<local>, C<lt>,
C<m>, C<map>, C<my>, C<ne>, C<next>, C<no>, C<or>, C<our>, C<package>,
C<print>, C<printf>, C<q>, C<qq>, C<qr>, C<qw>, C<qx>, C<redo>, C<require>,
C<return>, C<s>, C<say>, C<sort>, C<state>, C<sub>, C<tr>, C<unless>,
C<until>, C<use>, C<when>, C<while>, C<x>, C<xor>, C<y>

Calling with
ampersand syntax and through references does not work for the following
functions, as they have special syntax that cannot always be translated
into a simple list (e.g., C<eof> vs C<eof()>):

C<chdir>, C<chomp>, C<chop>, C<defined>, C<delete>, C<eof>, C<exec>,
C<exists>, C<lstat>, C<split>, C<stat>, C<system>, C<truncate>, C<unlink>

=head1 OVERRIDING CORE FUNCTIONS

To override a Perl built-in routine with your own version, you need to
import it at compile-time.  This can be conveniently achieved with the
C<subs> pragma.  This will affect only the package in which you've imported
the said subroutine:

    use subs 'chdir';
    sub chdir { ... }
    chdir $somewhere;

To override a built-in globally (that is, in all namespaces), you need to
import your function into the C<CORE::GLOBAL> pseudo-namespace at compile
time:

    BEGIN {
        *CORE::GLOBAL::hex = sub {
            # ... your code here
        };
    }

The new routine will be called whenever a built-in function is called
without a qualifying package:

    print hex("0x50"),"\n";			# prints 1

In both cases, if you want access to the original, unaltered routine, use
the C<CORE::> prefix:

    print CORE::hex("0x50"),"\n";		# prints 80

=head1 AUTHOR

This documentation provided by Tels <nospam-abuse@bloodgate.com> 2007.

=head1 SEE ALSO

L<perlsub>, L<perlfunc>.

=cut