101 lines
3.0 KiB
Perl
101 lines
3.0 KiB
Perl
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package bytes;
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our $VERSION = '1.04';
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$bytes::hint_bits = 0x00000008;
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sub import {
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$^H |= $bytes::hint_bits;
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}
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sub unimport {
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$^H &= ~$bytes::hint_bits;
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}
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sub AUTOLOAD {
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require "bytes_heavy.pl";
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goto &$AUTOLOAD if defined &$AUTOLOAD;
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require Carp;
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Carp::croak("Undefined subroutine $AUTOLOAD called");
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}
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sub length (_);
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sub chr (_);
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sub ord (_);
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sub substr ($$;$$);
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sub index ($$;$);
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sub rindex ($$;$);
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1;
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__END__
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=head1 NAME
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bytes - Perl pragma to force byte semantics rather than character semantics
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=head1 NOTICE
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This pragma reflects early attempts to incorporate Unicode into perl and
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has since been superseded. It breaks encapsulation (i.e. it exposes the
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innards of how the perl executable currently happens to store a string),
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and use of this module for anything other than debugging purposes is
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strongly discouraged. If you feel that the functions here within might be
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useful for your application, this possibly indicates a mismatch between
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your mental model of Perl Unicode and the current reality. In that case,
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you may wish to read some of the perl Unicode documentation:
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L<perluniintro>, L<perlunitut>, L<perlunifaq> and L<perlunicode>.
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=head1 SYNOPSIS
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use bytes;
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... chr(...); # or bytes::chr
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... index(...); # or bytes::index
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... length(...); # or bytes::length
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... ord(...); # or bytes::ord
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... rindex(...); # or bytes::rindex
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... substr(...); # or bytes::substr
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no bytes;
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=head1 DESCRIPTION
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The C<use bytes> pragma disables character semantics for the rest of the
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lexical scope in which it appears. C<no bytes> can be used to reverse
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the effect of C<use bytes> within the current lexical scope.
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Perl normally assumes character semantics in the presence of character
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data (i.e. data that has come from a source that has been marked as
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being of a particular character encoding). When C<use bytes> is in
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effect, the encoding is temporarily ignored, and each string is treated
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as a series of bytes.
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As an example, when Perl sees C<$x = chr(400)>, it encodes the character
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in UTF-8 and stores it in $x. Then it is marked as character data, so,
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for instance, C<length $x> returns C<1>. However, in the scope of the
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C<bytes> pragma, $x is treated as a series of bytes - the bytes that make
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up the UTF8 encoding - and C<length $x> returns C<2>:
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$x = chr(400);
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print "Length is ", length $x, "\n"; # "Length is 1"
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printf "Contents are %vd\n", $x; # "Contents are 400"
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{
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use bytes; # or "require bytes; bytes::length()"
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print "Length is ", length $x, "\n"; # "Length is 2"
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printf "Contents are %vd\n", $x; # "Contents are 198.144"
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}
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chr(), ord(), substr(), index() and rindex() behave similarly.
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For more on the implications and differences between character
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semantics and byte semantics, see L<perluniintro> and L<perlunicode>.
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=head1 LIMITATIONS
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bytes::substr() does not work as an lvalue().
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=head1 SEE ALSO
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L<perluniintro>, L<perlunicode>, L<utf8>
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=cut
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