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

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 the optional "finally" block part of 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.

The builtin namespace
  Introduced in Perl 5.36.0.

  Using certain functions of 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 was considered experimental until Perl 5.39.2. Some specific functions within it remain 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 tailor 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

try/catch control structure
  Introduced in Perl 5.34.0.

  Accepted in Perl 5.40 when not using the optional "finally" block.

The "const" attribute
  Introduced in Perl 5.22.0

  Accepted in Perl 5.40

  See also: "Constant Functions" in perlsub

for loop with multiple iteration variables
  Introduced in Perl 5.36.0.

  Accepted in Perl 5.40.

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

## 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@gmail.com>"

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

# COPYRIGHT

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

# LICENSE

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

2025-01-28 | perl v5.40.1