experimental - Experimental features made easy
use experimental 'lexical_subs', 'signatures';
my sub plus_one($value) { $value + 1 }
This pragma provides an easy and convenient way to enable or
disable experimental features.
Every version of perl has some number of features present but
considered "experimental." For much of the life of Perl 5, this
was only a designation found in the documentation. Starting in Perl v5.10.0,
and more aggressively in v5.18.0, experimental features were placed behind
pragmata used to enable the feature and disable associated warnings.
The "experimental" pragma exists
to combine the required incantations into a single interface stable across
releases of perl. For every experimental feature, this should enable the
feature and silence warnings for the enclosing lexical scope:
use experimental 'feature-name';
To disable the feature and, if applicable, re-enable any warnings,
use:
no experimental 'feature-name';
The supported features, documented further below, are:
- "args_array_with_signatures" - allow
@_ to be used in signatured subs.
This is supported on perl 5.20.0 and above, but is likely to
be removed in the future.
- "array_base" - allow the use of
$[ to change the starting index of
@array.
This was removed in perl 5.30.0.
- "autoderef" - allow push, each, keys,
and other built-ins on references.
This was added in perl 5.14.0 and removed in perl 5.24.0.
- "bitwise" - allow the new stringwise bit
operators
This was added in perl 5.22.0.
- "builtin" - allow the use of the
functions in the builtin:: namespace
This was added in perl 5.36.0
- "const_attr" - allow the :const
attribute on subs
This was added in perl 5.22.0.
- "declared_refs" - enables aliasing via
assignment to references
This was added in perl 5.26.0.
- "defer" - enables the use of defer
blocks
This was added in perl 5.36.0
- "extra_paired_delimiters" - enables the
use of more paired string delimiters than the traditional four,
"< >",
"( )",
"{ }", and
"[ ]".
This was added in perl 5.36.
- "for_list" - allows iterating over
multiple values at a time with "for"
This was added in perl 5.36.0
- "isa" - allow the use of the
"isa" infix operator
This was added in perl 5.32.0.
- "lexical_topic" - allow the use of
lexical $_ via "my
$_".
This was added in perl 5.10.0 and removed in perl 5.24.0.
- "lexical_subs" - allow the use of
lexical subroutines.
This was added in 5.18.0, and became non-experimental (and
always enabled) in 5.26.0.
- "postderef" - allow the use of postfix
dereferencing expressions
This was added in perl 5.20.0, and became non-experimental
(and always enabled) in 5.24.0.
- "postderef_qq" - allow the use of
postfix dereferencing expressions inside interpolating strings
This was added in perl 5.20.0, and became non-experimental
(and always enabled) in 5.24.0.
- "re_strict" - enables strict mode in
regular expressions
This was added in perl 5.22.0.
- "refaliasing" - allow aliasing via
"\$x = \$y"
This was added in perl 5.22.0.
- "regex_sets" - allow extended bracketed
character classes in regexps
This was added in perl 5.18.0, and became non-experimental
(and always enabled) in 5.36.0.
This is documented at "Extended Bracketed Character
Classes" in perlrecharclass.
- "signatures" - allow subroutine
signatures (for named arguments)
This was added in perl 5.20.0.
- "smartmatch" - allow the use of
"~~"
This was added in perl 5.10.0, but it should be noted there
are significant incompatibilities between 5.10.0 and 5.10.1.
The feature was deprecated in perl 5.38.0, and undeprecated in
5.42.0.
- "switch" - allow the use of
"~~", given, and when
This was added in perl 5.10.0.
The feature was deprecated in perl 5.38.0, and undeprecated in
5.42.0.
- "try" - allow the use of
"try" and
"catch"
This was added in perl 5.34.0
- "win32_perlio" - allows the use of the
:win32 IO layer.
This was added on perl 5.22.0.
Using this pragma to 'enable an experimental feature' is another
way of saying that this pragma will disable the warnings which would result
from using that feature. Therefore, the order in which pragmas are applied
is important. In particular, you probably want to enable experimental
features after you enable warnings:
use warnings;
use experimental 'smartmatch';
You also need to take care with modules that enable warnings for
you. A common example being Moose. In this example, warnings for the
'smartmatch' feature are first turned on by the warnings pragma, off by the
experimental pragma and back on again by the Moose module (fix is to switch
the last two lines):
use warnings;
use experimental 'smartmatch';
use Moose;
Because of the nature of the features it enables, forward
compatibility can not be guaranteed in any way.
perlexperiment contains more information about experimental
features.
Leon Timmermans <fawaka@gmail.com>
This software is copyright (c) 2013 by Leon Timmermans.
This is free software; you can redistribute it and/or modify it
under the same terms as the Perl 5 programming language system itself.