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Updated: Thursday, June 13, 2019

Internals (3)


Internals - Reserved special namespace for internals related functions


$is_ro= Internals::SvREADONLY($x)
$refcnt= Internals::SvREFCNT($x)


Perl Programmers Reference Guide                                  Internals(3)

       Internals - Reserved special namespace for internals related functions

           $is_ro= Internals::SvREADONLY($x)
           $refcnt= Internals::SvREFCNT($x)

       The Internals namespace is used by the core Perl development team to
       expose certain low level internals routines for testing and other

       In theory these routines were not and are not intended to be used
       outside of the perl core, and are subject to change and removal at any

       In practice people have come to depend on these over the years, despite
       being historically undocumented, so we will provide some level of
       forward compatibility for some time. Nevertheless you can assume that
       any routine documented here is experimental or deprecated and you
       should find alternatives to their use.

       SvREFCNT(THING [, $value])
           Historically Perl has been a refcounted language. This means that
           each variable tracks how many things reference it, and when the
           variable is no longer referenced it will automatically free itself.
           In theory Perl code should not have to care about this, and in a
           future version Perl might change to some other strategy, although
           in practice this is unlikely.

           This function allows one to violate the abstraction of variables
           and get or set the refcount of a variable, and in generally is
           really only useful in code that is testing refcount behavior.

           *NOTE* You are strongly discouraged from using this function in
           non-test code and especially discouraged from using the set form of
           this function.  The results of doing so may result in segmentation
           faults or other undefined behavior.

       SvREADONLY(THING, [, $value])
           Set or get whether a variable is readonly or not. Exactly what the
           readonly flag means depend on the type of the variable affected and
           the version of perl used.

           You are strongly discouraged from using this function directly. It
           is used by various core modules, like "Hash::Util", and the
           "constant" pragma to implement higher-level behavior which should
           be used instead.

           See the core implementation for the exact meaning of the readonly
           flag for each internal variable type.

           Clear any placeholders from a locked hash. Should not be used
           directly.  You should use the wrapper functions providewd by
           Hash::Util instead.  As of 5.25 also available as "
           Hash::Util::_clear_placeholders(%hash) "

       Perl core development team.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/perl-526      |
       |Stability      | Pass-through volatile |
       perlguts Hash::Util constant universal.c

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from

       Further information about this software can be found on the open source
       community website at http://www.perl.org/.

perl v5.26.3                      2018-03-23                      Internals(3)