Add a caveat about dereferencing slices

[perl/modules/autovivification.git] / lib / autovivification.pm

diff --git a/lib/autovivification.pm b/lib/autovivification.pm
index ac9bd98f0231308244a657d081563fcb0838bc45..ab0fc22668280726b6a1890c6f84a6afdf3b91f0 100644 (file)
--- a/lib/autovivification.pm
+++ b/lib/autovivification.pm
@@ -11,13 +11,13 @@ autovivification - Lexically disable autovivification.
 
 =head1 VERSION
 
-Version 0.01
+Version 0.03
 
 =cut
 
 our $VERSION;
 BEGIN {
- $VERSION = '0.01';
+ $VERSION = '0.03';
 }
 
 =head1 SYNOPSIS
@@ -65,6 +65,7 @@ Enables the features given in C<@opts>, which can be :
 C<'fetch'>
 
 Turn off autovivification for rvalue dereferencing expressions, such as C<< $value = $hashref->{key}[$idx]{$field} >>, C<< keys %{$hashref->{key}} >> or C<< values %{$hashref->{key}} >>.
+Starting from perl C<5.11>, it also covers C<leys> and C<values> on array references.
 When the expression would have autovivified, C<undef> is returned for a plain fetch, while C<keys> and C<values> return C<0> in scalar context and the empty list in list context.
 
 =item *
@@ -85,7 +86,7 @@ C<undef> is returned when the expression would have autovivified.
 
 C<'store'>
 
-Turn off autovivification for lvalue dereferencing expressions, such as C<< $hashref->{key}[$idx]{$field} = $value >>.
+Turn off autovivification for lvalue dereferencing expressions, such as C<< $hashref->{key}[$idx]{$field} = $value >> or C<< for ($hashref->{key}[$idx]{$field}) { ... } >>.
 An exception is thrown if vivification is needed to store the value, which means that effectively you can only assign to levels that are already defined (in the example, this would require C<< $hashref->{key}[$idx] >> to already be a hash reference).
 
 =item *
@@ -150,6 +151,12 @@ sub import {
  ();
 }
 
+=head1 CAVEATS
+
+The pragma doesn't apply when one dereferences the returned value of an array or hash slice, as in C<< @array[$id]->{member} >> or C<< @hash{$key}->{member} >>.
+This syntax is valid Perl, yet it's discouraged as the slice is here useless since the dereferencing enforces scalar context.
+If warnings are turned on, Perl will complain about one-element slices.
+
 =head1 DEPENDENCIES
 
 L<perl> 5.8.