Re: [perl #16834] Anomolous behaviour of SUBSTR() used as LValue

Message-ID: <7sfu+gzkg+AY092yn@efn.org>

p4raw-id: //depot/perl@19456

diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 6867857..d62f61a 100644 (file)
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -5461,6 +5461,16 @@ replacement string as the 4th argument.  This allows you to replace
 parts of the EXPR and return what was there before in one operation,
 just as you can with splice().
 
+If the lvalue returned by substr is used after the EXPR is changed in
+any way, the behaviour may not be as expected and is subject to change.
+This caveat includes code such as C<print(substr($foo,$a,$b)=$bar)> or
+C<(substr($foo,$a,$b)=$bar)=$fud> (where $foo is changed via the
+substring assignment, and then the substr is used again), or where a
+substr() is aliased via a C<foreach> loop or passed as a parameter or
+a reference to it is taken and then the alias, parameter, or deref'd
+reference either is used after the original EXPR has been changed or
+is assigned to and then used a second time.
+
 =item symlink OLDFILE,NEWFILE
 
 Creates a new filename symbolically linked to the old filename.