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

perlexperiment - A listing of experimental features in Perl

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.

Introduced in Perl 5.10.0

Modified in Perl 5.10.1, 5.12.0

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

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

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.

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

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

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

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

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

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.

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.

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

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.

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.

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.

Introduced in Perl 5.36.0

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

Introduced in Perl 5.36.0

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

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

my @array = qwX tinker tailer soldier spy X;

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

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
Introduced in Perl 5.005
Introduced in Perl 5.6.0

See also perldebug, perldebtut

Introduced in Perl 5.6.0
Introduced in Perl 5.6.0
Introduced in Perl 5.6.1

See also perlfork

Introduced in Perl 5.6.0

Accepted in Perl 5.8.0

Introduced in Perl 5.6.0

Accepted in Perl 5.8.1

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

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

Introduced in Perl 5.6.0

Accepted in Perl 5.20.0

See also perlsub

"(*ACCEPT)"

Introduced in Perl 5.10

Accepted in Perl 5.20.0

See also "PERLIO" in perlrun

Accepted in Perl 5.20.0

"\s" in regexp matches vertical tab
Accepted in Perl 5.22.0
Introduced in Perl 5.20.0

Accepted in Perl 5.24.0

Introduced in Perl 5.18.0

Accepted in Perl 5.26.0

Introduced in Perl 5.22.0

Accepted in Perl 5.28.0

Introduced in Perl 5.28.0

Accepted in Perl 5.32.0

Introduced in Perl 5.28.0

Accepted in Perl 5.32.0

Introduced in Perl 5.32.0

Accepted in Perl 5.36.0

Introduced in Perl 5.20.0

Accepted in Perl 5.36.0

Introduced in Perl 5.18

Accepted in Perl 5.36

See : "Extended Bracketed Character Classes" in perlrecharclass

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

Introduced in Perl 5.005

Moved from Perl 5.9.0 to CPAN

Introduced in Perl 5.6.0

Removed in Perl 5.9.0

"Getopt::Long" upgraded to version 2.35

Removed in Perl 5.8.8

The "-A" command line switch

Introduced in Perl 5.9.0

Removed in Perl 5.9.5

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

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

Introduced in Perl 5.10.0

Removed in Perl 5.24.0

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

Introduced in Perl 5.8.0 (or before)

Removed in Perl 5.36.0

For a complete list of features check feature.

brian d foy "<brian.d.foy@gmail.com>"

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

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

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

2022-05-29 perl v5.36.0