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.\" ========================================================================
.\"
.IX Title "Symbol 3"
.TH Symbol 3 "2007-03-30" "perl v5.8.8" "User Contributed Perl Documentation"
.SH "NAME"
Apache::Symbol \- Things for symbol things
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use Apache::Symbol ();
.Ve
.PP
.Vb 1
\& @ISA = qw(Apache::Symbol);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBperlsub/Constant Functions\fR says:
.PP
.Vb 6
\& If you redefine a subroutine which was eligible for inlining you'll get
\& a mandatory warning.  (You can use this warning to tell whether or not a
\& particular subroutine is considered constant.)  The warning is
\& considered severe enough not to be optional because previously compiled
\& invocations of the function will still be using the old value of the
\& function.
.Ve
.PP
\&\fImandatory warning\fR means there is _no_ way to avoid this warning 
no matter what tricks you pull in Perl.  This is bogus for us mod_perl
users when restarting the server with \fBPerlFreshRestart\fR on or when 
Apache::StatINC pulls in a module that has changed on disk.
.PP
You can, however, pull some tricks with \s-1XS\s0 to avoid this warning,
\&\fBApache::Symbol::undef\fR does just that.
.SH "ARGUMENTS"
.IX Header "ARGUMENTS"
\&\f(CW\*(C`undef_functions\*(C'\fR takes two arguments: \f(CW\*(C`skip\*(C'\fR and \f(CW\*(C`only_undef_exports\*(C'\fR.
.PP
\&\f(CW\*(C`skip\*(C'\fR is a regular expression indicating the function names to skip.
.PP
Use the \f(CW\*(C`only_undef_exports\*(C'\fR flag to undef only those functions
which are listed in \f(CW@EXPORT\fR, \f(CW@EXPORT_OK\fR, \f(CW%EXPORT_TAGS\fR, or
\&\f(CW@EXPORT_EXTRAS\fR.  \f(CW@EXPORT_EXTRAS\fR is not used by the Exporter, it
is only exists to communicate with \f(CW\*(C`undef_functions\*(C'\fR.
.PP
As a special case, if none of the \s-1EXPORT\s0 variables are defined ignore
\&\f(CW\*(C`only_undef_exports\*(C'\fR.  This takes care of trivial modules that don't
use the Exporter.
.SH "ARGUMENTS"
.IX Header "ARGUMENTS"
\&\f(CW\*(C`undef_functions\*(C'\fR takes two arguments: \f(CW\*(C`skip\*(C'\fR and \f(CW\*(C`only_undef_exports\*(C'\fR.
.PP
\&\f(CW\*(C`skip\*(C'\fR is a regular expression indicating the function names to skip.
.PP
Use the \f(CW\*(C`only_undef_exports\*(C'\fR flag to undef only those functions
which are listed in \f(CW@EXPORT\fR, \f(CW@EXPORT_OK\fR, \f(CW%EXPORT_TAGS\fR, or
\&\f(CW@EXPORT_EXTRAS\fR.  \f(CW@EXPORT_EXTRAS\fR is not used by the Exporter, it
is only exists to communicate with \f(CW\*(C`undef_functions\*(C'\fR.
.PP
As a special case, if none of the \s-1EXPORT\s0 variables are defined ignore
\&\f(CW\*(C`only_undef_exports\*(C'\fR.  This takes care of trivial modules that don't
use the Exporter.
.SH "PLAYERS"
.IX Header "PLAYERS"
This module and the undefining of functions is optional, if you wish
to have this functionality enabled, there are one or more switches you
need to know about.
.IP "PerlRestartHandler" 4
.IX Item "PerlRestartHandler"
Apache::Symbol defines a PerlRestartHandler which can be useful in
conjuction with \f(CW\*(C`PerlFreshRestart On\*(C'\fR as it will avoid subroutine
redefinition messages.  Configure like so:
.Sp
.Vb 1
\& PerlRestartHandler Apache::Symbol
.Ve
.IP "Apache::Registry" 4
.IX Item "Apache::Registry"
By placing the \s-1SYNOPSIS\s0 bit in you script, Apache::Registry will
undefine subroutines in your script before it is re-compiled to
avoid \*(L"subroutine re\-defined\*(R" warnings. 
.IP "Apache::StatINC" 4
.IX Item "Apache::StatINC"
See Apache::StatINC's docs.
.IP "\s-1APACHE_SYMBOL_UNIVERSAL\s0" 4
.IX Item "APACHE_SYMBOL_UNIVERSAL"
If this environment variable is true when Symbol.pm is compiled,
it will define UNIVERSAL::undef_functions, which means all classes
will inherit \fBApache::Symbol::undef_functions\fR.
.IP "Others" 4
.IX Item "Others"
Module such as \fBHTML::Embperl\fR and \fBApache::ePerl\fR who compile 
and script cache scripts ala Apache::Registry style can use  
\&\f(CW\*(C`undef_functions\*(C'\fR with this bit of code:
.Sp
.Vb 3
\&    if($package->can('undef_functions')) {
\&        $package->undef_functions;
\&    }
.Ve
.Sp
Where \f(CW$package\fR is the name of the package in which the script is
being re\-compiled.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIperlsub\fR\|(1), \fIDevel::Symdump\fR\|(3)
.SH "AUTHOR"
.IX Header "AUTHOR"
Doug MacEachern