Patch by Derek Price to Time::Piece for CPAN bug #21255:

NOTDATE - DATE should stringify DATE and let Perl handle things

p4raw-id: //depot/perl@29417

2 files changed, 31 insertions, 2 deletions

diff --git a/ext/Time/Piece/Piece.pm b/ext/Time/Piece/Piece.pm
index a3c4bfa31b..59b9976bc2 100644
--- a/ext/Time/Piece/Piece.pm
+++ b/ext/Time/Piece/Piece.pm
@@ -22,7 +22,7 @@ our %EXPORT_TAGS = (
     ':override' => 'internal',
     );
 
-our $VERSION = '1.11_01';
+our $VERSION = '1.11_02';
 
 bootstrap Time::Piece $VERSION;
 
@@ -540,7 +540,17 @@ sub subtract {
     if (UNIVERSAL::isa($rhs, 'Time::Seconds')) {
         $rhs = $rhs->seconds;
     }
-    die "Can't subtract a date from something!" if shift;
+
+    if (shift)
+    {
+	# SWAPED is set (so someone tried an expression like NOTDATE - DATE).
+	# Imitate Perl's standard behavior and return the result as if the
+	# string $time resolves to was subtracted from NOTDATE.  This way,
+	# classes which override this one and which have a stringify function
+	# that resolves to something that looks more like a number don't need
+	# to override this function.
+	return $rhs - "$time";
+    }
     
     if (UNIVERSAL::isa($rhs, 'Time::Piece')) {
         return Time::Seconds->new($time->epoch - $rhs->epoch);
diff --git a/ext/Time/Piece/t/06subclass.t b/ext/Time/Piece/t/06subclass.t
index 0a729d6c82..dce097a29b 100644
--- a/ext/Time/Piece/t/06subclass.t
+++ b/ext/Time/Piece/t/06subclass.t
@@ -45,3 +45,22 @@ for my $method (qw(new localtime gmtime)) {
   use base qw(Time::Piece);
   # this package is identical, but will be ->isa('Time::Piece::Twin');
 }
+
+{
+  my $class = "Time::Piece::NumString";
+  my $piece = $class->strptime ("2006", "%Y");
+  is (2007 - $piece, 1,
+      "subtract attempts stringify for unrecognized objects.");
+}
+
+## Below is a package which only changes the stringify function.
+{
+  package Time::Piece::NumString;
+  use base qw(Time::Piece);
+  use overload '""' => \&_stringify;
+  sub _stringify
+  {
+    my $self = shift;
+    return $self->strftime ("%Y");
+  }
+}