X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2Fconstant.pm;h=5d3dd91b46f94f01999fd9eed46aab737dfe0ed8;hb=4499d6b9d14594604210bc28005c5e4ab2e49947;hp=4416cf2ade5df748e79d325bc06c02bdbc8d1f60;hpb=acce7d4e04d89207299003c3e80c69d50bc82069;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/lib/constant.pm b/lib/constant.pm
index 4416cf2..5d3dd91 100644
--- a/lib/constant.pm
+++ b/lib/constant.pm
@@ -20,6 +20,18 @@ constant - Perl pragma to declare constants
 
     print "This line does nothing"		unless DEBUGGING;
 
+    # references can be declared constant
+    use constant CHASH		=> { foo => 42 };
+    use constant CARRAY		=> [ 1,2,3,4 ];
+    use constant CPSEUDOHASH	=> [ { foo => 1}, 42 ];
+    use constant CCODE		=> sub { "bite $_[0]\n" };
+
+    print CHASH->{foo};
+    print CARRAY->[$i];
+    print CPSEUDOHASH->{foo};
+    print CCODE->("me");
+    print CHASH->[10];				# compile-time error
+
 =head1 DESCRIPTION
 
 This will declare a symbol to be a constant with the given scalar
@@ -80,11 +92,14 @@ B<necessarily> that value in the current implementation.
 
 Magical values, tied values, and references can be made into
 constants at compile time, allowing for way cool stuff like this.
+(These error numbers aren't totally portable, alas.)
 
     use constant E2BIG => ($! = 7);
     print   E2BIG, "\n";	# something like "Arg list too long"
     print 0+E2BIG, "\n";	# "7"
 
+Errors in dereferencing constant references are trapped at compile-time.
+
 =head1 TECHNICAL NOTE
 
 In the current implementation, scalar constants are actually
@@ -105,6 +120,15 @@ name as a constant. This is probably a Good Thing.
 Unlike constants in some languages, these cannot be overridden
 on the command line or via environment variables.
 
+You can get into trouble if you use constants in a context which
+automatically quotes barewords (as is true for any subroutine call).
+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'>.
+
 =head1 AUTHOR
 
 Tom Phoenix, E<lt>F<rootbeer@teleport.com>E<gt>, with help from
@@ -126,7 +150,7 @@ use vars qw($VERSION);
 #=======================================================================
 
 # Some of this stuff didn't work in version 5.003, alas.
-require 5.003_20;
+require 5.003_96;
 
 #=======================================================================
 # import() - import symbols into user's namespace