latest switch/say/~~

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

package bytes;

our $VERSION = '1.02';

$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 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