Internals(3perl) - phpMan

Internals(3perl)                 Perl Programmers Reference Guide                Internals(3perl)

NAME
       Internals - Reserved special namespace for internals related functions

SYNOPSIS
           $is_ro= Internals::SvREADONLY($x)
           $refcnt= Internals::SvREFCNT($x)
           hv_clear_placeholders(%hash);

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

       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 time.

       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.

   FUNCTIONS
       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.

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

AUTHOR
       Perl core development team.

SEE ALSO
       perlguts Hash::Util constant universal.c

perl v5.34.0                                2025-07-25                           Internals(3perl)

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