Re: Should keys in pseudo-hashes -always- exist? [DOC PATCH]

To: perl5-porters@perl.org
Message-ID: <19991003023401.A1520@blackrider>

p4raw-id: //depot/cfgperl@4293

diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index a09c6e5..d07ded3 100644 (file)
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -1412,6 +1412,9 @@ This surprising autovivification in what does not at first--or even
 second--glance appear to be an lvalue context may be fixed in a future
 release.
 
+See L<perlref/"Pseudo-hashes"> for specifics on how exists() acts when
+used on a pseudo-hash.
+
 =item exit EXPR
 
 Evaluates EXPR and exits immediately with that value.    Example:

diff --git a/pod/perlref.pod b/pod/perlref.pod
index 5958a72..08a2b42 100644 (file)
--- a/pod/perlref.pod
+++ b/pod/perlref.pod
@@ -563,6 +563,25 @@ or try to access nonexistent fields.  For better performance, Perl can also
 do the translation from field names to array indices at compile time for
 typed object references.  See L<fields>.
 
+There are two ways to check for the existance of a key in a
+pseudo-hash.  The first is to use exists().  This checks to see if the
+given field has been used yet.  It acts this way to match the behavior
+of a regular hash.  For instance:
+
+       $phash = [{foo =>, bar => 2, pants => 3}, 'FOO'];
+       $phash->{pants} = undef;
+
+       exists $phash->{foo};    # true, 'foo' was set in the declaration
+       exists $phash->{bar};    # false, 'bar' has not been used.
+       exists $phash->{pants};  # true, your 'pants' have been touched
+
+The second is to use exists() on the hash reference sitting in the
+first array element.  This checks to see if the given key is a valid
+field in the pseudo-hash.
+
+       exists $phash->[0]{pants};      # true, 'pants' is a valid field
+       exists $phash->[0]{shoes};      # false, 'shoes' can't be used
+
 =head2 Function Templates
 
 As explained above, a closure is an anonymous function with access to the