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48 lines
1.2 KiB
XML
48 lines
1.2 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<sect1 xml:id="language.types.singleton">
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<title>Singleton types</title>
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<para>
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Singleton types are those which allow only one value.
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PHP has support for two singleton types:
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<type>false</type> as of PHP 8.0.0 and <type>true</type>
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as of PHP 8.2.0.
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</para>
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<warning>
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<simpara>
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Prior to PHP 8.2.0 the <type>false</type> type
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could only be used as part of a
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<link linkend="language.types.type-system.composite.union">union type</link>.
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</simpara>
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</warning>
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<note>
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<simpara>
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It is not possible to define custom singleton types. Consider using an
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<link linkend="language.types.enumerations">enumerations</link> instead.
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</simpara>
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</note>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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