1experimental(3)       User Contributed Perl Documentation      experimental(3)
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NAME

6       experimental - Experimental features made easy
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VERSION

9       version 0.027
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SYNOPSIS

12        use experimental 'lexical_subs', 'signatures';
13        my sub plus_one($value) { $value + 1 }
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DESCRIPTION

16       This pragma provides an easy and convenient way to enable or disable
17       experimental features.
18
19       Every version of perl has some number of features present but
20       considered "experimental."  For much of the life of Perl 5, this was
21       only a designation found in the documentation.  Starting in Perl
22       v5.10.0, and more aggressively in v5.18.0, experimental features were
23       placed behind pragmata used to enable the feature and disable
24       associated warnings.
25
26       The "experimental" pragma exists to combine the required incantations
27       into a single interface stable across releases of perl.  For every
28       experimental feature, this should enable the feature and silence
29       warnings for the enclosing lexical scope:
30
31         use experimental 'feature-name';
32
33       To disable the feature and, if applicable, re-enable any warnings, use:
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35         no experimental 'feature-name';
36
37       The supported features, documented further below, are:
38
39       •   "args_array_with_signatures" - allow @_ to be used in signatured
40           subs.
41
42           This is supported on perl 5.20.0 and above, but is likely to be
43           removed in the future.
44
45       •   "array_base" - allow the use of $[ to change the starting index of
46           @array.
47
48           This was removed in perl 5.30.0.
49
50       •   "autoderef" - allow push, each, keys, and other built-ins on
51           references.
52
53           This was added in perl 5.14.0 and removed in perl 5.24.0.
54
55       •   "bitwise" - allow the new stringwise bit operators
56
57           This was added in perl 5.22.0.
58
59       •   "builtin" - allow the use of the functions in the builtin::
60           namespace
61
62           This was added in perl 5.36.0
63
64       •   "const_attr" - allow the :const attribute on subs
65
66           This was added in perl 5.22.0.
67
68       •   "declared_refs" - enables aliasing via assignment to references
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70           This was added in perl 5.26.0.
71
72       •   "defer" - enables the use of defer blocks
73
74           This was added in perl 5.36.0
75
76       •   "for_list" - allows iterating over multiple values at a time with
77           "for"
78
79           This was added in perl 5.36.0
80
81       •   "isa" - allow the use of the "isa" infix operator
82
83           This was added in perl 5.32.0.
84
85       •   "lexical_topic" - allow the use of lexical $_ via "my $_".
86
87           This was added in perl 5.10.0 and removed in perl 5.24.0.
88
89       •   "lexical_subs" - allow the use of lexical subroutines.
90
91           This was added in 5.18.0.
92
93       •   "postderef" - allow the use of postfix dereferencing expressions
94
95           This was added in perl 5.20.0, and became non-experimental (and
96           always enabled) in 5.24.0.
97
98       •   "postderef_qq" - allow the use of postfix dereferencing expressions
99           inside interpolating strings
100
101           This was added in perl 5.20.0, and became non-experimental (and
102           always enabled) in 5.24.0.
103
104       •   "re_strict" - enables strict mode in regular expressions
105
106           This was added in perl 5.22.0.
107
108       •   "refaliasing" - allow aliasing via "\$x = \$y"
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110           This was added in perl 5.22.0.
111
112       •   "regex_sets" - allow extended bracketed character classes in
113           regexps
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115           This was added in perl 5.18.0.
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117       •   "signatures" - allow subroutine signatures (for named arguments)
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119           This was added in perl 5.20.0.
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121       •   "smartmatch" - allow the use of "~~"
122
123           This was added in perl 5.10.0, but it should be noted there are
124           significant incompatibilities between 5.10.0 and 5.10.1.
125
126       •   "switch" - allow the use of "~~", given, and when
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128           This was added in perl 5.10.0.
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130       •   "try" - allow the use of "try" and "catch"
131
132           This was added in perl 5.34.0
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134       •   "win32_perlio" - allows the use of the :win32 IO layer.
135
136           This was added on perl 5.22.0.
137
138   Ordering matters
139       Using this pragma to 'enable an experimental feature' is another way of
140       saying that this pragma will disable the warnings which would result
141       from using that feature.  Therefore, the order in which pragmas are
142       applied is important.  In particular, you probably want to enable
143       experimental features after you enable warnings:
144
145         use warnings;
146         use experimental 'smartmatch';
147
148       You also need to take care with modules that enable warnings for you.
149       A common example being Moose.  In this example, warnings for the
150       'smartmatch' feature are first turned on by the warnings pragma, off by
151       the experimental pragma and back on again by the Moose module (fix is
152       to switch the last two lines):
153
154         use warnings;
155         use experimental 'smartmatch';
156         use Moose;
157
158   Disclaimer
159       Because of the nature of the features it enables, forward compatibility
160       can not be guaranteed in any way.
161

SEE ALSO

163       perlexperiment contains more information about experimental features.
164

AUTHOR

166       Leon Timmermans <leont@cpan.org>
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169       This software is copyright (c) 2013 by Leon Timmermans.
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171       This is free software; you can redistribute it and/or modify it under
172       the same terms as the Perl 5 programming language system itself.
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176perl v5.34.0                      2022-02-09                   experimental(3)
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