perlexperiment - A listing of experimental features in Perl

- NAME
- DESCRIPTION
  - Current experiments
  - Accepted features
  - Removed features
- SEE ALSO
- AUTHORS
- COPYRIGHT
- LICENSE

# 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].

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].

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].

  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].

  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]

  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].

  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].

(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].

  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].

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].

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]

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].

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].

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].

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].

## 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@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.

perlexperiment - A listing of experimental features in Perl