man > PERLEXPERIMENT(1)

PERLEXPERIMENT(1)                 Perl Programmers Reference Guide                 PERLEXPERIMENT(1)

NAME
       perlexperiment - A listing of experimental features in Perl

DESCRIPTION
       This document lists the current and past experimental features in the perl core. Although all
       of these are documented with their appropriate topics, this succinct listing gives you an
       overview and basic facts about their status.

       So far we've merely tried to find and list the experimental features and infer their
       inception, versions, etc. There's a lot of speculation here.

   Current experiments
       Smart match ("~~")
               Introduced in Perl 5.10.0

               Modified in Perl 5.10.1, 5.12.0

               Deprecated in 5.38.0

               Will be removed in 5.42.0

               Using this feature triggers warnings in the category "deprecated".

               The       ticket       for       this      experiment      is      [perl      #13173]
               <https://github.com/Perl/perl5/issues/13173>.

       Pluggable keywords
               Introduced in Perl 5.11.2

               See "PL_keyword_plugin" in perlapi for the mechanism.

               The      ticket      for      this      experiment       is       [perl       #13199]
               <https://github.com/Perl/perl5/issues/13199>.

       Aliasing via reference
               Introduced in Perl 5.22.0

               Using this feature triggers warnings in the category "experimental::refaliasing".

               The       ticket       for       this      experiment      is      [perl      #14150]
               <https://github.com/Perl/perl5/issues/14150>.

               See also: "Assigning to References" in perlref

       The "const" attribute
               Introduced in Perl 5.22.0

               Using this feature triggers warnings in the category "experimental::const_attr".

               The      ticket      for      this      experiment       is       [perl       #14428]
               <https://github.com/Perl/perl5/issues/14428>.

               See also: "Constant Functions" in perlsub

       use re 'strict';
               Introduced in Perl 5.22.0

               Using this feature triggers warnings in the category "experimental::re_strict".

               The       ticket       for       this      experiment      is      [perl      #18755]
               <https://github.com/Perl/perl5/issues/18755>

               See "'strict' mode" in re

       Declaring a reference to a variable
               Introduced in Perl 5.26.0

               Using this feature triggers warnings in the category "experimental::declared_refs".

               The      ticket      for      this      experiment       is       [perl       #15458]
               <https://github.com/Perl/perl5/issues/15458>.

               See also: "Declaring a Reference to a Variable" in perlref

       There is an "installhtml" target in the Makefile.
               The       ticket       for       this      experiment      is      [perl      #12726]
               <https://github.com/Perl/perl5/issues/12726>.

       (Limited) Variable-length look-behind
               Introduced in Perl 5.30.0.

               Variability of up to 255 characters is handled.

               Using this feature triggers warnings in the category "experimental::vlb".

               The      ticket      for      this      experiment       is       [perl       #18756]
               <https://github.com/Perl/perl5/issues/18756>.

               See       also:       "(*positive_lookbehind:pattern)"       in       perlre      and
               "(*negative_lookbehind:pattern)" in perlre

       Unicode private use character hooks
               Introduced in Perl 5.30.0.

               This feature is part of an interface intended for internal and  experimental  use  by
               the perl5 developers.  You are unlikely to encounter it in the wild.

               Using this feature triggers warnings in the category "experimental::private_use".

               The       ticket       for       this      experiment      is      [perl      #18758]
               <https://github.com/Perl/perl5/issues/18758>.

       Unicode property wildcards
               Introduced in Perl 5.30.0.

               This feature allows regular expression matching against Unicode character  properties
               to be expressed more concisely.

               Using      this      feature      triggers      warnings      in     the     category
               "experimental::uniprop_wildcards".

               The      ticket      for      this      experiment       is       [perl       #18759]
               <https://github.com/Perl/perl5/issues/18759>.

       try/catch control structure
               Introduced in Perl 5.34.0.

               Using this feature triggers warnings in the category "experimental::try".

               The       ticket       for       this      experiment      is      [perl      #18760]
               <https://github.com/Perl/perl5/issues/18760>

       Use of @_ within subroutine signatures
               Introduced in Perl 5.36.0 as part  of  a  reduction  in  the  scope  of  experimental
               subroutine signatures.

               Using  the default arguments array (@_) within a subroutine that uses signatures will
               emit a  warning  in  the  category  "experimental::args_array_with_signatures".  This
               includes  @_  directly,  elements  of  it such as $_[$index], or situations where the
               default arguments array is accessed implicitly  such  as  "shift"  or  "pop"  without
               arguments.

       for loop with multiple iteration variables
               Introduced in Perl 5.36.0.

               Using this feature triggers warnings in the category "experimental::for_list".

               This  feature  enables  a  parenthesized list of iteration variables for "for" rather
               than a single variable.

               The      ticket      for      this      experiment       is       [perl       #18744]
               <https://github.com/Perl/perl5/issues/18744>.

       The builtin namespace
               Introduced in Perl 5.36.0.

               Using this feature triggers warnings in the category "experimental::builtin".

               In  Perl  5.36.0, a new namespace, "builtin", was created for new core functions that
               will not be present in every namespace, but will be  available  for  importing.   The
               namespace  itself is considered an experiment.  Specific functions within it may also
               be experimental.

               The      ticket      for      this      experiment       is       [perl       #19764]
               <https://github.com/Perl/perl5/issues/19764>.

       The defer block modifier
               Introduced in Perl 5.36.0

               Using this feature triggers warnings in the category "experimental::defer".

               This  feature  adds  a new kind of block, a "defer" block, which will not be executed
               until the containing block is being exited.

               The      ticket      for      this      experiment       is       [perl       #17949]
               <https://github.com/Perl/perl5/issues/17949>.

       Extra paired delimiters for quote-like operators
               Introduced in Perl 5.36.0

               Using      this      feature      triggers      warnings      in     the     category
               "experimental::extra_paired_delimiters".

               This feature allows for many non-ASCII pairs of mirroring delimiters, for example:

                   my @array = qw« tinker tailer soldier spy »;

               The      ticket      for      this      experiment       is       [perl       #19765]
               <https://github.com/Perl/perl5/issues/19765>.

   Accepted features
       These  features  were  so wildly successful and played so well with others that we decided to
       remove their experimental status and admit them as full, stable  features  in  the  world  of
       Perl,  lavishing  all  the benefits and luxuries thereof.  They are also awarded +5 Stability
       and +3 Charisma.

       64-bit support
               Introduced in Perl 5.005

       die accepts a reference
               Introduced in Perl 5.005

       DB module
               Introduced in Perl 5.6.0

               See also perldebug, perldebtut

       Weak references
               Introduced in Perl 5.6.0

       Internal file glob
               Introduced in Perl 5.6.0

       fork() emulation
               Introduced in Perl 5.6.1

               See also perlfork

       -Dusemultiplicity -Duseithreads
               Introduced in Perl 5.6.0

               Accepted in Perl 5.8.0

       Support for long doubles
               Introduced in Perl 5.6.0

               Accepted in Perl 5.8.1

       The "\N" regex character class
               The "\N" character class, not to  be  confused  with  the  named  character  sequence
               "\N{NAME}", denotes any non-newline character in a regular expression.

               Introduced in Perl 5.12

               Exact version of acceptance unclear, but no later than Perl 5.18.

       "(?{code})" and "(??{ code })"
               Introduced in Perl 5.6.0

               Accepted in Perl 5.20.0

               See also perlre

       Linux abstract Unix domain sockets
               Introduced in Perl 5.9.2

               Accepted before Perl 5.20.0.  The Socket library is now primarily maintained on CPAN,
               rather than in the perl core.

               See also Socket

       Lvalue subroutines
               Introduced in Perl 5.6.0

               Accepted in Perl 5.20.0

               See also perlsub

       Backtracking control verbs
               "(*ACCEPT)"

               Introduced in Perl 5.10

               Accepted in Perl 5.20.0

       The ":pop" IO pseudolayer
               See also "PERLIO" in perlrun

               Accepted in Perl 5.20.0

       "\s" in regexp matches vertical tab
               Accepted in Perl 5.22.0

       Postfix dereference syntax
               Introduced in Perl 5.20.0

               Accepted in Perl 5.24.0

       Lexical subroutines
               Introduced in Perl 5.18.0

               Accepted in Perl 5.26.0

       String- and number-specific bitwise operators
               Introduced in Perl 5.22.0

               Accepted in Perl 5.28.0

       Alphabetic assertions
               Introduced in Perl 5.28.0

               Accepted in Perl 5.32.0

       Script runs
               Introduced in Perl 5.28.0

               Accepted in Perl 5.32.0

       The infix "isa" operator
               Introduced in Perl 5.32.0

               Accepted in Perl 5.36.0

       Subroutine signatures
               Introduced in Perl 5.20.0

               Accepted in Perl 5.36.0

       Regular Expression Set Operations
               Introduced in Perl 5.18

               Accepted in Perl 5.36

               See : "Extended Bracketed Character Classes" in perlrecharclass

   Removed features
       These features are no longer considered experimental and their functionality has disappeared.
       It's your own fault if you wrote production programs using these features after we explicitly
       told you not to (see perlpolicy).

       5.005-style threading
               Introduced in Perl 5.005

               Removed in Perl 5.10

       perlcc  Introduced in Perl 5.005

               Moved from Perl 5.9.0 to CPAN

       The pseudo-hash data type
               Introduced in Perl 5.6.0

               Removed in Perl 5.9.0

       GetOpt::Long Options can now take multiple values at once (experimental)
               "Getopt::Long" upgraded to version 2.35

               Removed in Perl 5.8.8

       Assertions
               The "-A" command line switch

               Introduced in Perl 5.9.0

               Removed in Perl 5.9.5

       Test::Harness::Straps
               Moved from Perl 5.10.1 to CPAN

       "legacy"
               The experimental "legacy" pragma was swallowed by the "feature" pragma.

               Introduced in Perl 5.11.2

               Removed in Perl 5.11.3

       Lexical $_
               Using this feature triggered warnings in the category "experimental::lexical_topic".

               Introduced in Perl 5.10.0

               Removed in Perl 5.24.0

       Array and hash container functions accept references
               Using this feature triggered warnings in the category "experimental::autoderef".

               Superseded by "Postfix dereference syntax".

               Introduced in Perl 5.14.0

               Removed in Perl 5.24.0

       "our" can have an experimental optional attribute "unique"
               Introduced in Perl 5.8.0

               Deprecated in Perl 5.10.0

               Removed in Perl 5.28.0

       The ":win32" IO pseudolayer
               Introduced in Perl 5.8.0 (or before)

               Removed in Perl 5.36.0

SEE ALSO
       For a complete list of features check feature.

AUTHORS
       brian d foy "<brian.d.foy AT gmail.com>"

       Sébastien Aperghis-Tramoni "<saper AT cpan.org>"

COPYRIGHT
       Copyright 2010, brian d foy "<brian.d.foy AT gmail.com>"

LICENSE
       You can use and redistribute this document under the same terms as Perl itself.

perl v5.38.2                                 2026-08-18                            PERLEXPERIMENT(1)