144 lines
4.6 KiB
Perl
144 lines
4.6 KiB
Perl
# ==================================================================
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# Gossamer Threads Module Library - http://gossamer-threads.com/
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#
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# constants
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# Author: Jason Rhinelander
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# CVS Info : 087,071,086,086,085
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# $Id: constants.pm,v 1.9 2004/01/13 01:35:15 jagerman Exp $
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#
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# Copyright (c) 2004 Gossamer Threads Inc. All Rights Reserved.
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# ==================================================================
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#
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# Description:
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# Lightweight version of the standard constant.pm that allows you
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# to declare multiple scalar constants in a single compile-time
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# command. Like constant.pm, these scalar constants are optimized
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# during Perl's compilation stage.
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# Unlike constant.pm, this does not allow you to declare list
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# constants.
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package constants;
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use strict;
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use Carp;
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use vars qw($VERSION);
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$VERSION = '1.00';
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#=======================================================================
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# Some of this stuff didn't work in version 5.003, alas.
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require 5.003_96;
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#=======================================================================
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# import() - import symbols into user's namespace
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#
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# What we actually do is define a function in the caller's namespace
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# which returns the value. The function we create will normally
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# be inlined as a constant, thereby avoiding further sub calling
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# overhead.
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#=======================================================================
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sub import {
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my $class = shift;
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@_ or return; # Ignore 'use constant;'
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my %constants = @_;
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my $pkg = caller;
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{
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no strict 'refs';
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for my $name (keys %constants) {
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croak qq{Can't define "$name" as constant} .
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qq{ (name contains invalid characters or is empty)}
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unless $name =~ /^[^\W_0-9]\w*$/;
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my $scalar = $constants{$name};
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*{"${pkg}::$name"} = sub () { $scalar };
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}
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}
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}
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1;
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__END__
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=head1 NAME
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constants - Perl pragma to declare multiple scalar constants at once
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=head1 SYNOPSIS
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use constants BUFFER_SIZE => 4096,
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ONE_YEAR => 365.2425 * 24 * 60 * 60,
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PI => 4 * atan2 1, 1,
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DEBUGGING => 0,
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ORACLE => 'oracle@cs.indiana.edu',
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USERNAME => scalar getpwuid($<);
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sub deg2rad { PI * $_[0] / 180 }
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print "This line does nothing" unless DEBUGGING;
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# references can be declared constants
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use constants CHASH => { foo => 42 },
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CARRAY => [ 1,2,3,4 ],
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CPSEUDOHASH => [ { foo => 1}, 42 ],
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CCODE => sub { "bite $_[0]\n" };
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print CHASH->{foo};
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print CARRAY->[$i];
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print CPSEUDOHASH->{foo};
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print CCODE->("me");
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print CHASH->[10]; # compile-time error
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=head1 DESCRIPTION
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This will declare a symbol to be a constant with the given scalar
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value. This module mimics constant.pm in every way, except that it
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allows multiple scalar constants to be created simultaneously. To
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create constant list values you should use constant.
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See L<constant> for details about how constants work.
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=head1 NOTES
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The value or values are evaluated in a list context, so you should
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override this if needed with C<scalar> as shown above.
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=head1 TECHNICAL NOTE
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In the current implementation, scalar constants are actually
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inlinable subroutines. As of version 5.004 of Perl, the appropriate
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scalar constant is inserted directly in place of some subroutine
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calls, thereby saving the overhead of a subroutine call. See
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L<perlsub/"Constant Functions"> for details about how and when this
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happens.
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=head1 BUGS
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In the current version of Perl, list constants are not inlined
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and some symbols may be redefined without generating a warning.
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It is not possible to have a subroutine or keyword with the same
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name as a constant. This is probably a Good Thing.
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Unlike constants in some languages, these cannot be overridden
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on the command line or via environment variables.
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You can get into trouble if you use constants in a context which
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automatically quotes barewords (as is true for any subroutine call).
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For example, you can't say C<$hash{CONSTANT}> because C<CONSTANT> will
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be interpreted as a string. Use C<$hash{CONSTANT()}> or
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C<$hash{+CONSTANT}> to prevent the bareword quoting mechanism from
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kicking in. Similarly, since the C<=E<gt>> operator quotes a bareword
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immediately to its left you have to say C<CONSTANT() =E<gt> 'value'>
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instead of C<CONSTANT =E<gt> 'value'>.
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=head1 AUTHOR
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constant.pm: Tom Phoenix, E<lt>F<rootbeer@teleport.com>E<gt>, with help from
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many other folks.
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constants.pm: Jason Rhinelander, Gossamer Threads Inc.
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=cut
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