Change 13356 by jhi@alpha on 2001/11/29 13:39:06
Subject: Re: [PATCH Exporter.pm] Explain dangers & workaround for AUTOLOADed
constant subs
From: Tels <[EMAIL PROTECTED]>
Date: Thu, 29 Nov 2001 07:28:10 +0100 (CET)
Message-Id: <[EMAIL PROTECTED]>
(plus paragraph rewrapping)
Affected files ...
.... //depot/perl/lib/Exporter.pm#18 edit
Differences ...
==== //depot/perl/lib/Exporter.pm#18 (text) ====
Index: perl/lib/Exporter.pm
--- perl/lib/Exporter.pm.~1~ Thu Nov 29 06:45:05 2001
+++ perl/lib/Exporter.pm Thu Nov 29 06:45:05 2001
@@ -309,16 +309,17 @@
=head2 C<AUTOLOAD>ed Constants
-Many modules make use of C<AUTOLOAD>ing for constant subroutines to avoid
-having to compile and waste memory on rarely used values (see L<perlsub> for
-details on constant subroutines). Calls to such constant subroutines are not
-optimized away at compile time because they can't be checked at compile time
-for constancy.
+Many modules make use of C<AUTOLOAD>ing for constant subroutines to
+avoid having to compile and waste memory on rarely used values (see
+L<perlsub> for details on constant subroutines). Calls to such
+constant subroutines are not optimized away at compile time because
+they can't be checked at compile time for constancy.
-Even if a prototype is available at compile time, the body of the subroutine is
-not (it hasn't been C<AUTOLOAD>ed yet). perl needs to examine both the C<()>
-prototype and the body of a subroutine at compile time to detect that it can
-safely replace calls to that subroutine with the constant value.
+Even if a prototype is available at compile time, the body of the
+subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
+examine both the C<()> prototype and the body of a subroutine at
+compile time to detect that it can safely replace calls to that
+subroutine with the constant value.
A workaround for this is to call the constants once in a C<BEGIN> block:
@@ -330,11 +331,11 @@
BEGIN { SO_LINGER }
foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
-This forces the C<AUTOLOAD> for C<SOLINGER> to take place before SO_LINGER is
-encountered later in C<My> package.
+This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
+SO_LINGER is encountered later in C<My> package.
-If you are writing a package that C<AUTOLOAD>s, consider forcing an C<AUTOLOAD>
-for any constants explicitly imported by other packages or which are usually
-used when your package is C<use>d.
+If you are writing a package that C<AUTOLOAD>s, consider forcing
+an C<AUTOLOAD> for any constants explicitly imported by other packages
+or which are usually used when your package is C<use>d.
=cut
End of Patch.
