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Document readonly classes #1996

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Merged
merged 4 commits into from
Nov 12, 2022
Merged

Document readonly classes #1996

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c1e566f
Document readonly classes
Girgias Nov 11, 2022
dd59f36
Link to readonly prop
Girgias Nov 12, 2022
3e57ac1
Reference class for attribute
Girgias Nov 12, 2022
3b6b054
Wording + Markup and add extending constraint
Girgias Nov 12, 2022
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66 changes: 66 additions & 0 deletions language/oop5/basic.xml
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Expand Up @@ -125,6 +125,72 @@ Stack trace:
</screen>
</example>
</warning>

<sect3 xml:id="language.oop5.basic.class.readonly">
<title>Readonly classes</title>
<para>
As of PHP 8.2.0, a class can be marked with the
<modifier>readonly</modifier> modifier.
Marking a class as <modifier>readonly</modifier> will add the
<link linkend="language.oop5.properties.readonly-properties"><modifier>readonly</modifier> modifier</link>
to every declared property, and prevent the creation of
<link linkend="language.oop5.properties.dynamic-properties">dynamic properties</link>.
Moreover, it is impossible to add support for them by using the
<classname>AllowDynamicProperties</classname> attribute. Attempting to do so
will trigger a compile-time error.
</para>
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maybe you could mention that readonly classes can extend only readonly classes, and non-readonly classes cannot extend readonly ones either.

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Added a paragraph :)

<example>
<programlisting role="php">
<![CDATA[
<?php
#[AllowDynamicProperties]
readonly class Foo {
}

// Fatal error: Cannot apply #[AllowDynamicProperties] to readonly class Foo
?>
]]>
</programlisting>
</example>

<para>
As neither untyped, nor static properties can be marked with the
<literal>readonly</literal> modifier, readonly classes cannot declare
them either:
</para>
<example>
<programlisting role="php">
<![CDATA[
<?php
readonly class Foo
{
public $bar;
}

// Fatal error: Readonly property Foo::$bar must have type
?>
]]>
</programlisting>
<programlisting role="php">
<![CDATA[
<?php
readonly class Foo
{
public static int $bar;
}

// Fatal error: Readonly class Foo cannot declare static properties
?>
]]>
</programlisting>
</example>
<para>
A <modifier>readonly</modifier> class can be
<link linkend="language.oop5.basic.extends">extended</link>
if, and only if, the child class is also a
<modifier>readonly</modifier> class.
</para>
</sect3>
</sect2>

<sect2 xml:id="language.oop5.basic.new">
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