feature - Perl pragma to enable new features

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This pragma provides a way to minimize that risk. New syntactic constructs, or new semantic meanings to older constructs, can be enabled by <code>use feature 'foo'</code>, and will be parsed only when the appropriate feature pragma is in scope.</p> <h2 id="Lexical-effect"><a class="permalink" href="#Lexical-effect">#</a><a id="Lexical"></a>Lexical effect</h2> <p>Like other pragmas (<code>use strict</code>, for example), features have a lexical effect. <code>use feature qw(foo)</code> will only make the feature "foo" available from that point to the end of the enclosing block.</p> <pre><code>{ use feature 'say'; say "say is available here"; } print "But not here.\n";</code></pre> <h2 id="no-feature"><a class="permalink" href="#no-feature">#</a><a id="no"></a><code>no feature</code></h2> <p>Features can also be turned off by using <code>no feature "foo"</code>. This too has lexical effect.</p> <pre><code>use feature 'say'; say "say is available here"; { no feature 'say'; print "But not here.\n"; } say "Yet it is here.";</code></pre> <p><code>no feature</code> with no features specified will turn off all features.</p> <h2 id="The-'switch'-feature"><a class="permalink" href="#The-'switch'-feature">#</a><a id="The"></a><a id="The-switch-feature"></a>The 'switch' feature</h2> <p><code>use feature 'switch'</code> tells the compiler to enable the Perl 6 given/when construct.</p> <p>See <a href="/5.12.1/perlsyn#Switch-statements">"Switch statements" in perlsyn</a> for details.</p> <h2 id="The-'say'-feature"><a class="permalink" href="#The-'say'-feature">#</a><a id="The1"></a><a id="The-say-feature"></a>The 'say' feature</h2> <p><code>use feature 'say'</code> tells the compiler to enable the Perl 6 <code>say</code> function.</p> <p>See <a href="/5.12.1/perlfunc#say">"say" in perlfunc</a> for details.</p> <h2 id="the-'state'-feature"><a class="permalink" href="#the-'state'-feature">#</a><a id="the"></a><a id="the-state-feature"></a>the 'state' feature</h2> <p><code>use feature 'state'</code> tells the compiler to enable <code>state</code> variables.</p> <p>See <a href="/5.12.1/perlsub#Persistent-Private-Variables">"Persistent Private Variables" in perlsub</a> for details.</p> <h2 id="the-'unicode_strings'-feature"><a class="permalink" href="#the-'unicode_strings'-feature">#</a><a id="the1"></a><a id="the-unicode_strings-feature"></a>the 'unicode_strings' feature</h2> <p><code>use feature 'unicode_strings'</code> tells the compiler to treat all strings outside of <code>use locale</code> and <code>use bytes</code> as Unicode. It is available starting with Perl 5.11.3.</p> <p>See <a href="/5.12.1/perlunicode#The-%22Unicode-Bug%22">"The "Unicode Bug"" in perlunicode</a> for details.</p> <h1 id="FEATURE-BUNDLES"><a class="permalink" href="#FEATURE-BUNDLES">#</a><a id="FEATURE"></a>FEATURE BUNDLES</h1> <p>It's possible to load a whole slew of features in one go, using a <i>feature bundle</i>. The name of a feature bundle is prefixed with a colon, to distinguish it from an actual feature. At present, the only feature bundle is <code>use feature ":5.10"</code> which is equivalent to <code>use feature qw(switch say state)</code>.</p> <p>Specifying sub-versions such as the <code>0</code> in <code>5.10.0</code> in feature bundles has no effect: feature bundles are guaranteed to be the same for all sub-versions.</p> <h1 id="IMPLICIT-LOADING"><a class="permalink" href="#IMPLICIT-LOADING">#</a><a id="IMPLICIT"></a>IMPLICIT LOADING</h1> <p>There are two ways to load the <code>feature</code> pragma implicitly :</p> <ul> <li><p>By using the <code>-E</code> switch on the command-line instead of <code>-e</code>. It enables all available features in the main compilation unit (that is, the one-liner.)</p> </li> <li><p>By requiring explicitly a minimal Perl version number for your program, with the <code>use VERSION</code> construct, and when the version is higher than or equal to 5.10.0. That is,</p> <pre><code>use 5.10.0;</code></pre> <p>will do an implicit</p> <pre><code>use feature ':5.10';</code></pre> <p>and so on. Note how the trailing sub-version is automatically stripped from the version.</p> <p>But to avoid portability warnings (see <a href="/5.12.1/perlfunc#use">"use" in perlfunc</a>), you may prefer:</p> <pre><code>use 5.010;</code></pre> <p>with the same effect.</p> </li> </ul> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via the <a href="https://github.com/Perl/perl5/issues">Perl issue tracker</a>, the <a href="https://lists.perl.org/list/perl5-porters.html">mailing list</a>, or <a href="https://kiwiirc.com/client/irc.perl.org/p5p">IRC</a> to report any issues with the contents or format of the documentation.</p> </div> </div> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.slim.min.js" integrity="sha512-/DXTXr6nQodMUiq+IUJYCt2PPOUjrHJ9wFrqpJ3XkgPNOZVfMok7cRw6CSxyCQxXn6ozlESsSh1/sMCTF1rL/g==" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.1/umd/popper.min.js" integrity="sha512-ubuT8Z88WxezgSqf3RLuNi5lmjstiJcyezx34yIU2gAHonIi27Na7atqzUZCOoY4CExaoFumzOsFQ2Ch+I/HCw==" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script> <script src="/js/highlight.pack.js"></script> <script>hljs.highlightAll();</script> </body> </html>

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feature - Perl pragma to enable new features - Perldoc Browser