XS(3) User Contributed Perl Documentation XS(3)
Readonly::XS - Companion module for Readonly.pm, to speed up read-only scalar variables.
This document describes version 1.05 of Readonly::XS, February 24, 2009.
Install this module, but do not use it.
The Readonly module (q.v.) is an effective way to create non-modifiable variables.
However, it's relatively slow.
The reason it's slow is that is implements the read-only-ness of variables via tied
objects. This mechanism is inherently slow. Perl simply has to do a lot of work under
the hood to make tied variables work.
This module corrects the speed problem, at least with respect to scalar variables. When
Readonly::XS is installed, Readonly uses it to access the internals of scalar variables.
Instead of creating a scalar variable object and tying it, Readonly simply flips the
SvREADONLY bit in the scalar's FLAGS structure.
Readonly arrays and hashes are not sped up by this, since the SvREADONLY flag only works
for scalars. Arrays and hashes always use the tie interface.
Why implement this as a separate module? Because not everyone can use XS. Not everyone
has a C compiler. Also, installations with a statically-linked perl may not want to
recompile their perl binary just for this module. Rather than render Readonly.pm useless
these people, the XS portion was put into a separate module.
Programs that you write do not need to know whether Readonly::XS is installed or not.
They should just "use Readonly" and let Readonly worry about whether or not it can use XS.
If the Readonly::XS is present, Readonly will be faster. If not, it won't. Either way,
it will still work, and your code will not have to change.
Your program can check whether Readonly.pm is using XS or not by examining the
$Readonly::XSokay variable. It will be true if the XS module was found and is being used.
Please do not change this variable.
AUTHOR / COPYRIGHT
Eric Roode, email@example.com
Copyright (c) 2003-2009 by Eric J. Roode. All Rights Reserved. This module is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.
To avoid my spam filter, please include "Perl", "module", or this module's name in the
message's subject line, and/or GPG-sign your message.
perl v5.16.3 2009-02-24 XS(3)