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.
perl v5.40.1 2026-08-30 PERLEXPERIMENT(1)
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