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https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@350015 c90b9560-bf6c-de11-be94-00142212c4b1
359 lines
9.6 KiB
XML
359 lines
9.6 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<sect1 xml:id="language.oop5.properties" xmlns="http://docbook.org/ns/docbook">
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<title>Properties</title>
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<para>
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Class member variables are called <emphasis>properties</emphasis>. You may also see
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them referred to using other terms such as <emphasis>attributes</emphasis> or
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<emphasis>fields</emphasis>, but for the purposes of this reference we will use
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<emphasis>properties</emphasis>. They are defined by using one of the
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keywords <literal>public</literal>, <literal>protected</literal>,
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or <literal>private</literal>, optionally followed by a type declaration,
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followed by a normal variable declaration. This declaration may
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include an initialization, but this initialization must be a constant
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value--that is, it must be able to be evaluated at compile time and
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must not depend on run-time information in order to be evaluated.
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</para>
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<para>
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See <xref linkend="language.oop5.visibility" /> for more
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information on the meanings
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of <literal>public</literal>, <literal>protected</literal>,
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and <literal>private</literal>.
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</para>
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<note>
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<para>
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In order to maintain backward compatibility with PHP 4, PHP 5 will
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still accept the use of the keyword <literal>var</literal> in
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property declarations instead of (or in addition
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to) <literal>public</literal>, <literal>protected</literal>,
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or <literal>private</literal>. However, <literal>var</literal> is
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no longer required. In versions of PHP from 5.0 to 5.1.3, the use
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of <literal>var</literal> was considered deprecated and would
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issue an <constant>E_STRICT</constant> warning, but since PHP
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5.1.3 it is no longer deprecated and does not issue the warning.
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</para>
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<para>
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If you declare a property using <literal>var</literal> instead of
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one of <literal>public</literal>, <literal>protected</literal>,
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or <literal>private</literal>, then PHP 5 will treat the property
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as if it had been declared as <literal>public</literal>.
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</para>
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</note>
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<para>
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Within class methods non-static properties may be accessed by using
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<literal>-></literal> (Object Operator): <varname>$this->property</varname>
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(where <literal>property</literal> is the name of the property).
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Static properties are accessed by using the <literal>::</literal> (Double Colon):
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<varname>self::$property</varname>. See <link linkend="language.oop5.static">Static Keyword</link>
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for more information on the difference between static and non-static properties.
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</para>
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<para>
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The pseudo-variable <varname>$this</varname> is available inside
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any class method when that method is called from within an object
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context. <varname>$this</varname> is a reference to the calling
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object (usually the object to which the method belongs, but
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possibly another object, if the method is called
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<link linkend="language.oop5.static">statically</link> from the context
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of a secondary object).
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</para>
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<para>
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<example>
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<title>property declarations</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class SimpleClass
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{
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// valid as of PHP 5.6.0:
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public $var1 = 'hello ' . 'world';
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// valid as of PHP 5.3.0:
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public $var2 = <<<EOD
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hello world
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EOD;
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// valid as of PHP 5.6.0:
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public $var3 = 1+2;
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// invalid property declarations:
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public $var4 = self::myStaticMethod();
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public $var5 = $myVar;
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// valid property declarations:
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public $var6 = myConstant;
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public $var7 = array(true, false);
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// valid as of PHP 5.3.0:
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public $var8 = <<<'EOD'
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hello world
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EOD;
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}
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<note>
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<para>
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There are some nice functions to handle classes and objects. You
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might want to take a look at
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the <link linkend="ref.classobj">Class/Object Functions</link>.
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</para>
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</note>
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<sect2 xml:id="language.oop5.properties.heredoc-nowdoc">
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<title>Heredoc and Nowdoc</title>
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<para>
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As of PHP 5.3.0
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<link linkend="language.types.string.syntax.heredoc">heredocs</link> and
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<link linkend="language.types.string.syntax.nowdoc">nowdocs</link>
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can be used in any static data context, including property
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declarations.
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<example>
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<title>Example of using a nowdoc to initialize a property</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class foo {
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// As of PHP 5.3.0
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public $bar = <<<'EOT'
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bar
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EOT;
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public $baz = <<<EOT
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baz
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EOT;
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}
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<note>
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<para>
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Nowdoc and Heredoc support was added in PHP 5.3.0.
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</para>
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</note>
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</sect2>
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<sect2 xml:id="language.oop5.properties.typed-properties">
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<title>Type declarations</title>
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<para>
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As of PHP 7.4.0, property definitions can include a type declaration.
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<example>
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<title>Example of typed properties</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class User
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{
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public int $id;
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public ?string $name;
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public function __construct(int $id, ?string $name)
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{
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$this->id = $id;
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$this->name = $name;
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}
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}
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$user = new User(1234, null);
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var_dump($user->id);
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var_dump($user->name);
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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int(1234)
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NULL
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]]>
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</screen>
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</example>
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</para>
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<para>
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Typed properties must be initialized before accessing, otherwise an
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<classname>Error</classname> is thrown.
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<example>
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<title>Accessing properties</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class Shape
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{
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public int $numberOfSides;
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public string $name;
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public function setNumberOfSides(int $numberOfSides): void
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{
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$this->numberOfSides = $numberOfSides;
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}
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public function setName(string $name): void
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{
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$this->name = $name;
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}
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public function getNumberOfSides(): int
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{
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return $this->numberOfSides;
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}
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public function getName(): string
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{
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return $this->name;
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}
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}
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$triangle = new Shape();
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$triangle->setName("triangle");
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$triangle->setNumberofSides(3);
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var_dump($triangle->getName());
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var_dump($triangle->getNumberOfSides());
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$circle = new Shape();
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$circle->setName("circle");
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var_dump($circle->getName());
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var_dump($circle->getNumberOfSides());
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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string(8) "triangle"
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int(3)
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string(6) "circle"
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Fatal error: Uncaught Error: Typed property Shape::$numberOfSides must not be accessed before initialization
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]]>
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</screen>
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</example>
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</para>
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<sect3 xml:id="language.oop5.properties.typed-properties.valid-types">
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<title>Valid property types</title>
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<informaltable>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Type</entry>
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<entry>Description</entry>
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<entry>Minimum PHP version</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><type>bool</type></entry>
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<entry>
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The property must be <type>boolean</type> value.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><type>int</type></entry>
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<entry>
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The property must be an <type>integer</type>.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><type>float</type></entry>
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<entry>
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The property must be a <type>float</type>ing point number.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><type>string</type></entry>
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<entry>
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The property must be a <type>string</type>.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><type>array</type></entry>
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<entry>
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The property must be an <type>array</type>.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><literal>object</literal></entry>
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<entry>
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The property must be an <type>object</type>.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><literal>iterable</literal></entry>
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<entry>
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The property must be either an <type>array</type> or an &instanceof;
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<interfacename>Traversable</interfacename>.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><literal>self</literal></entry>
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<entry>
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The property must be an &instanceof; the same class in which the
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property is defined.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry><literal>parent</literal></entry>
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<entry>
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The property must be an &instanceof; the parent class of the class
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in which the property is defined.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry>Class/interface name</entry>
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<entry>
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The property must be an &instanceof; the given class or interface
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name.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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<row>
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<entry>?type</entry>
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<entry>
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The property must be the specified type, or &null;.
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</entry>
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<entry>PHP 7.4.0</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</sect3>
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</sect2>
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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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