SCALAR/FIRSTKEY for tied hashes in scalar context

[p5sagit/p5-mst-13.2.git] / pod / perltie.pod

diff --git a/pod/perltie.pod b/pod/perltie.pod
index b81a51b..468855c 100644 (file)
--- a/pod/perltie.pod
+++ b/pod/perltie.pod
@@ -474,7 +474,8 @@ the constructor.  FETCH and STORE access the key and value pairs.  EXISTS
 reports whether a key is present in the hash, and DELETE deletes one.
 CLEAR empties the hash by deleting all the key and value pairs.  FIRSTKEY
 and NEXTKEY implement the keys() and each() functions to iterate over all
-the keys.  UNTIE is called when C<untie> happens, and DESTROY is called when
+the keys. SCALAR is triggered when the tied hash is evaluated in scalar 
+context. UNTIE is called when C<untie> happens, and DESTROY is called when
 the tied variable is garbage collected.
 
 If this seems like a lot, then feel free to inherit from merely the
@@ -757,6 +758,25 @@ thing, but we'll have to go through the LIST field indirectly.
        return each %{ $self->{LIST} }
     }
 
+=item SCALAR this
+
+This is called when the hash is evaluated in scalar context. In order
+to mimic the behaviour of untied hashes, this method should return a
+false value when the tied hash is considered empty. If this method does
+not exist, perl will make some educated guesses and return false when
+the hash is not inside an iteration. In this case, FIRSTKEY is called
+and the result will be a false value if FIRSTKEY returns the empty list,
+true otherwise.
+
+In our example we can just call C<scalar> on the underlying hash
+referenced by C<$self-E<gt>{LIST}>:
+
+    sub SCALAR {
+       carp &whowasi if $DEBUG;
+       my $self = shift;
+       return scalar %{ $self->{LIST} }
+    }
+
 =item UNTIE this
 
 This is called when C<untie> occurs.  See L<The C<untie> Gotcha> below.
@@ -1107,4 +1127,6 @@ TIEHANDLE by Sven Verdoolaege <F<skimo@dns.ufsia.ac.be>> and Doug MacEachern <F<
 
 UNTIE by Nick Ing-Simmons <F<nick@ing-simmons.net>>
 
+SCALAR by Tassilo von Parseval <F<tassilo.von.parseval@rwth-aachen.de>>
+
 Tying Arrays by Casey West <F<casey@geeknest.com>>