diff options
Diffstat (limited to 'contrib/perl5/lib/constant.pm')
| -rw-r--r-- | contrib/perl5/lib/constant.pm | 196 |
1 files changed, 144 insertions, 52 deletions
diff --git a/contrib/perl5/lib/constant.pm b/contrib/perl5/lib/constant.pm index 5d3dd91..72ad793 100644 --- a/contrib/perl5/lib/constant.pm +++ b/contrib/perl5/lib/constant.pm @@ -1,6 +1,107 @@ package constant; -$VERSION = '1.00'; +use strict; +use 5.005_64; +use warnings::register; + +our($VERSION, %declared); +$VERSION = '1.02'; + +#======================================================================= + +# Some names are evil choices. +my %keywords = map +($_, 1), qw{ BEGIN INIT CHECK END DESTROY AUTOLOAD }; + +my %forced_into_main = map +($_, 1), + qw{ STDIN STDOUT STDERR ARGV ARGVOUT ENV INC SIG }; + +my %forbidden = (%keywords, %forced_into_main); + +#======================================================================= +# import() - import symbols into user's namespace +# +# What we actually do is define a function in the caller's namespace +# which returns the value. The function we create will normally +# be inlined as a constant, thereby avoiding further sub calling +# overhead. +#======================================================================= +sub import { + my $class = shift; + return unless @_; # Ignore 'use constant;' + my $name = shift; + unless (defined $name) { + require Carp; + Carp::croak("Can't use undef as constant name"); + } + my $pkg = caller; + + # Normal constant name + if ($name =~ /^_?[^\W_0-9]\w*\z/ and !$forbidden{$name}) { + # Everything is okay + + # Name forced into main, but we're not in main. Fatal. + } elsif ($forced_into_main{$name} and $pkg ne 'main') { + require Carp; + Carp::croak("Constant name '$name' is forced into main::"); + + # Starts with double underscore. Fatal. + } elsif ($name =~ /^__/) { + require Carp; + Carp::croak("Constant name '$name' begins with '__'"); + + # Maybe the name is tolerable + } elsif ($name =~ /^[A-Za-z_]\w*\z/) { + # Then we'll warn only if you've asked for warnings + if (warnings::enabled()) { + if ($keywords{$name}) { + warnings::warn("Constant name '$name' is a Perl keyword"); + } elsif ($forced_into_main{$name}) { + warnings::warn("Constant name '$name' is " . + "forced into package main::"); + } else { + # Catch-all - what did I miss? If you get this error, + # please let me know what your constant's name was. + # Write to <rootbeer@redcat.com>. Thanks! + warnings::warn("Constant name '$name' has unknown problems"); + } + } + + # Looks like a boolean + # use constant FRED == fred; + } elsif ($name =~ /^[01]?\z/) { + require Carp; + if (@_) { + Carp::croak("Constant name '$name' is invalid"); + } else { + Carp::croak("Constant name looks like boolean value"); + } + + } else { + # Must have bad characters + require Carp; + Carp::croak("Constant name '$name' has invalid characters"); + } + + { + no strict 'refs'; + my $full_name = "${pkg}::$name"; + $declared{$full_name}++; + if (@_ == 1) { + my $scalar = $_[0]; + *$full_name = sub () { $scalar }; + } elsif (@_) { + my @list = @_; + *$full_name = sub () { @list }; + } else { + *$full_name = sub () { }; + } + } + +} + +1; + +__END__ =head1 NAME @@ -20,7 +121,7 @@ constant - Perl pragma to declare constants print "This line does nothing" unless DEBUGGING; - # references can be declared constant + # references can be constants use constant CHASH => { foo => 42 }; use constant CARRAY => [ 1,2,3,4 ]; use constant CPSEUDOHASH => [ { foo => 1}, 42 ]; @@ -30,7 +131,7 @@ constant - Perl pragma to declare constants print CARRAY->[$i]; print CPSEUDOHASH->{foo}; print CCODE->("me"); - print CHASH->[10]; # compile-time error + print CHASH->[10]; # compile-time error =head1 DESCRIPTION @@ -63,7 +164,10 @@ List constants are returned as lists, not as arrays. The use of all caps for constant names is merely a convention, although it is recommended in order to make constants stand out and to help avoid collisions with other barewords, keywords, and -subroutine names. Constant names must begin with a letter. +subroutine names. Constant names must begin with a letter or +underscore. Names beginning with a double underscore are reserved. Some +poor choices for names will generate warnings, if warnings are enabled at +compile time. Constant symbols are package scoped (rather than block scoped, as C<use strict> is). That is, you can refer to a constant from package @@ -98,7 +202,24 @@ constants at compile time, allowing for way cool stuff like this. print E2BIG, "\n"; # something like "Arg list too long" print 0+E2BIG, "\n"; # "7" -Errors in dereferencing constant references are trapped at compile-time. +Dereferencing constant references incorrectly (such as using an array +subscript on a constant hash reference, or vice versa) will be trapped at +compile time. + +In the rare case in which you need to discover at run time whether a +particular constant has been declared via this module, you may use +this function to examine the hash C<%constant::declared>. If the given +constant name does not include a package name, the current package is +used. + + sub declared ($) { + use constant 1.01; # don't omit this! + my $name = shift; + $name =~ s/^::/main::/; + my $pkg = caller; + my $full_name = $name =~ /::/ ? $name : "${pkg}::$name"; + $constant::declared{$full_name}; + } =head1 TECHNICAL NOTE @@ -115,7 +236,19 @@ In the current version of Perl, list constants are not inlined and some symbols may be redefined without generating a warning. It is not possible to have a subroutine or keyword with the same -name as a constant. This is probably a Good Thing. +name as a constant in the same package. This is probably a Good Thing. + +A constant with a name in the list C<STDIN STDOUT STDERR ARGV ARGVOUT +ENV INC SIG> is not allowed anywhere but in package C<main::>, for +technical reasons. + +Even though a reference may be declared as a constant, the reference may +point to data which may be changed, as this code shows. + + use constant CARRAY => [ 1,2,3,4 ]; + print CARRAY->[1]; + CARRAY->[1] = " be changed"; + print CARRAY->[1]; Unlike constants in some languages, these cannot be overridden on the command line or via environment variables. @@ -126,61 +259,20 @@ For example, you can't say C<$hash{CONSTANT}> because C<CONSTANT> will be interpreted as a string. Use C<$hash{CONSTANT()}> or C<$hash{+CONSTANT}> to prevent the bareword quoting mechanism from kicking in. Similarly, since the C<=E<gt>> operator quotes a bareword -immediately to its left you have to say C<CONSTANT() =E<gt> 'value'> -instead of C<CONSTANT =E<gt> 'value'>. +immediately to its left, you have to say C<CONSTANT() =E<gt> 'value'> +(or simply use a comma in place of the big arrow) instead of +C<CONSTANT =E<gt> 'value'>. =head1 AUTHOR -Tom Phoenix, E<lt>F<rootbeer@teleport.com>E<gt>, with help from +Tom Phoenix, E<lt>F<rootbeer@redcat.com>E<gt>, with help from many other folks. =head1 COPYRIGHT -Copyright (C) 1997, Tom Phoenix +Copyright (C) 1997, 1999 Tom Phoenix This module is free software; you can redistribute it or modify it under the same terms as Perl itself. =cut - -use strict; -use Carp; -use vars qw($VERSION); - -#======================================================================= - -# Some of this stuff didn't work in version 5.003, alas. -require 5.003_96; - -#======================================================================= -# import() - import symbols into user's namespace -# -# What we actually do is define a function in the caller's namespace -# which returns the value. The function we create will normally -# be inlined as a constant, thereby avoiding further sub calling -# overhead. -#======================================================================= -sub import { - my $class = shift; - my $name = shift or return; # Ignore 'use constant;' - croak qq{Can't define "$name" as constant} . - qq{ (name contains invalid characters or is empty)} - unless $name =~ /^[^\W_0-9]\w*$/; - - my $pkg = caller; - { - no strict 'refs'; - if (@_ == 1) { - my $scalar = $_[0]; - *{"${pkg}::$name"} = sub () { $scalar }; - } elsif (@_) { - my @list = @_; - *{"${pkg}::$name"} = sub () { @list }; - } else { - *{"${pkg}::$name"} = sub () { }; - } - } - -} - -1; |
