Re: Deleting undef values from a hash

[Zaxo]

I agree that a documentation patch is the best response. Since the value for a key can be literally any scalar, it is impossible to think of a return value that would serve to distinguish between the two cases (at least without some perl magic).

We can imagine delete returning a hash or a list of key-value pairs, but (besides breaking compatibility) that would injure idioms that are more useful than knowledge of which keys existed before a deletion. The idiom for re-keying a value, $foo{'bar'} = delete $foo{'baz'}; would be wrecked, for instance.

A workaround can be devised pretty easily if we need the existence information, my @actual_values = delete @a{ grep { exists $a{$_}} @somekeys}; There are lots of variations possible on that snippet.

[liz]

Rafael applied my documentation patch yesterday:

-Returns each element so deleted or the undefined value if there was n
+o such
-element.  Deleting from C<$ENV{}> modifies the environment.  Deleting
+ from
+Returns a list with the same number of elements as the number of elem
+ents
+for which deletion was B<attempted>.  Each element of that list consi
+sts of
+either the value of the element deleted, or the undefined value.  In 
+scalar
+context, this means that you get the value of the last element delete
+d (or
+the undefined value if that element did not exist).
+
+    %HASH = (foo => 11, bar => 22, baz => 33);
+    $scalar = delete $HASH{foo};            # $scalar is 11
+    $scalar = delete @HASH{qw(foo bar)};    # $scalar is 22
+    @array  = delete @HASH{qw(foo bar baz)} # @array  is (undef,undef
+,33)
+
+Deleting from C<$ENV{}> modifies the environment.  Deleting from
 a hash tied to a DBM file deletes the entry from the DBM file.  Delet
+ing
 from a C<tie>d hash or array may not necessarily return anything.

Liz