doc f7abe7

[p5sagit/p5-mst-13.2.git] / lib / bytes.pm

package bytes;

our $VERSION = '1.04';

$bytes::hint_bits = 0x00000008;

sub import {
    $^H |= $bytes::hint_bits;
}

sub unimport {
    $^H &= ~$bytes::hint_bits;
}

sub AUTOLOAD {
    require "bytes_heavy.pl";
    goto &$AUTOLOAD if defined &$AUTOLOAD;
    require Carp;
    Carp::croak("Undefined subroutine $AUTOLOAD called");
}

sub length (_);
sub chr (_);
sub ord (_);
sub substr ($$;$$);
sub index ($$;$);
sub rindex ($$;$);

1;
__END__

=head1 NAME

bytes - Perl pragma to force byte semantics rather than character semantics

=head1 NOTICE

This pragma reflects early attempts to incorporate Unicode into perl and
has since been superseded. It breaks encapsulation (i.e. it exposes the
innards of how the perl executable currently happens to store a string),
and use of this module for anything other than debugging purposes is
strongly discouraged. If you feel that the functions here within might be
useful for your application, this possibly indicates a mismatch between
your mental model of Perl Unicode and the current reality. In that case,
you may wish to read some of the perl Unicode documentation:
L<perluniintro>, L<perlunitut>, L<perlunifaq> and L<perlunicode>.

=head1 SYNOPSIS

    use bytes;
    ... chr(...);       # or bytes::chr
    ... index(...);     # or bytes::index
    ... length(...);    # or bytes::length
    ... ord(...);       # or bytes::ord
    ... rindex(...);    # or bytes::rindex
    ... substr(...);    # or bytes::substr
    no bytes;


=head1 DESCRIPTION

The C<use bytes> pragma disables character semantics for the rest of the
lexical scope in which it appears.  C<no bytes> can be used to reverse
the effect of C<use bytes> within the current lexical scope.

Perl normally assumes character semantics in the presence of character
data (i.e. data that has come from a source that has been marked as
being of a particular character encoding). When C<use bytes> is in
effect, the encoding is temporarily ignored, and each string is treated
as a series of bytes. 

As an example, when Perl sees C<$x = chr(400)>, it encodes the character
in UTF-8 and stores it in $x. Then it is marked as character data, so,
for instance, C<length $x> returns C<1>. However, in the scope of the
C<bytes> pragma, $x is treated as a series of bytes - the bytes that make
up the UTF8 encoding - and C<length $x> returns C<2>:

    $x = chr(400);
    print "Length is ", length $x, "\n";     # "Length is 1"
    printf "Contents are %vd\n", $x;         # "Contents are 400"
    { 
        use bytes; # or "require bytes; bytes::length()"
        print "Length is ", length $x, "\n"; # "Length is 2"
        printf "Contents are %vd\n", $x;     # "Contents are 198.144"
    }

chr(), ord(), substr(), index() and rindex() behave similarly.

For more on the implications and differences between character
semantics and byte semantics, see L<perluniintro> and L<perlunicode>.

=head1 LIMITATIONS

bytes::substr() does not work as an lvalue().

=head1 SEE ALSO

L<perluniintro>, L<perlunicode>, L<utf8>

=cut