Re: Hash key created by subroutine call? (fwd)

On Mon, 24 Feb 1997 06:20:14 MST, Tom Christiansen wrote:
>Considering how frequently this gets asked, how about
>putting it in perlsub?
>
>------- start of forwarded message -------
>From: Rick Smith <ricks@sd.znet.com>
>Newsgroups: comp.lang.perl.misc
>Subject: Hash key created by subroutine call?
>Date: Sat, 22 Feb 1997 21:47:52 -0800

I seem to be in a documental state today.

p5p-msgid: <199702242229.RAA04395@aatma.engin.umich.edu>

1 files changed, 20 insertions, 0 deletions

diff --git a/pod/perltrap.pod b/pod/perltrap.pod
index 05cb02b47b..a179b8b5a8 100644
--- a/pod/perltrap.pod
+++ b/pod/perltrap.pod
@@ -1137,6 +1137,26 @@ general subroutine traps.  Includes some OS-Specific traps.
 
 =over 5
 
+=item * Subroutine calls provide lvalue context to arguments
+
+Beginning with version 5.002, all subroutine arguments are consistently
+given a "value may be modified" context, since all subroutines are able
+to modify their arguments by explicitly referring to C<$_[0]> etc.
+This means that any array and hash elements provided as arguments
+will B<always be created> if they did not exist at the time
+the subroutine is called.  (perl5 versions before 5.002 used to provide
+lvalue context for the second and subsequent arguments, and perl4 did
+not provide lvalue context to subroutine arguments at all--even though
+arguments were supposedly modifiable in perl4).
+
+    sub test { $_[0] = 1; $_[1] = 2; $_[2] = 3; }
+    &test($foo{'bar'}, $bar{'foo'}, $foo[5]);
+    print join(':', %foo), '|', join(':',%bar), '|', join(':',@foo);
+    
+    # perl4          prints: ||
+    # perl5 <  5.002 prints: |foo:2|:::::3
+    # perl5 >= 5.002 prints: bar:1|foo:2|:::::3
+
 =item * (Signals)
 
 Barewords that used to look like strings to Perl will now look like subroutine