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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<chapter xml:id="language.types" xmlns="http://docbook.org/ns/docbook">
<title>Types</title>
<sect1 xml:id="language.types.intro">
<title>Introduction</title>
<para>
Every single expression in PHP has one of the following
built-in types depending on its value:
<itemizedlist>
<listitem><simpara><type>null</type></simpara></listitem>
<listitem><simpara><type>bool</type></simpara></listitem>
<listitem><simpara><type>int</type></simpara></listitem>
<listitem><simpara><type>float</type> (floating-point number)</simpara></listitem>
<listitem><simpara><type>string</type></simpara></listitem>
<listitem><simpara><type>array</type></simpara></listitem>
<listitem><simpara><type>object</type></simpara></listitem>
<listitem><simpara><type>callable</type></simpara></listitem>
<listitem><simpara><type>resource</type></simpara></listitem>
</itemizedlist>
</para>
<para>
PHP is a dynamically typed language, which means that by default there is
no need to specify the type of a variable, as this will be determined at
runtime. However, it is possible to statically type some aspect of the
language via the use of
<link linkend="language.types.declarations">type declarations</link>.
Different types that are supported by PHP's type system can be found at the
<link linkend="language.types.type-system">type system</link> page.
</para>
<para>
Types restrict the kind of operations that can be performed on them.
However, if an expression/variable is used in an operation which
its type does not support, PHP will attempt to
<link linkend="language.types.type-juggling">type juggle</link>
the value into a type that supports the operation.
This process depends on the context in which the value is used.
For more information, see the section on
<link linkend="language.types.type-juggling">Type Juggling</link>.
</para>
<tip>
<simpara>
<link linkend="types.comparisons">The type comparison tables</link>
may also be useful, as various examples of comparison between values of
different types are present.
</simpara>
</tip>
<note>
<simpara>
It is possible to force an expression to be evaluated to a certain type by
using a <link linkend="language.types.typecasting">type cast</link>.
A variable can also be type cast in-place by using the
<function>settype</function> function on it.
</simpara>
</note>
<para>
To check the value and type of an
<link linkend="language.expressions">expression</link>,
use the <function>var_dump</function> function.
To retrieve the type of an
<link linkend="language.expressions">expression</link>,
use the <function>get_debug_type</function> function.
However, to check if an expression is of a certain type use the
<!-- TODO When PhD support is there: <function>is_<replaceable>type</replaceable></function> -->
<literal>is_<replaceable>type</replaceable></literal> functions instead.
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
$a_bool = true; // a bool
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an int
echo get_debug_type($a_bool), "\n";
echo get_debug_type($a_str), "\n";
// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}
var_dump($an_int);
// If $a_bool is a string, print it out
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>
]]>
</programlisting>
&example.outputs.8;
<screen>
<![CDATA[
bool
string
int(16)
]]>
</screen>
</informalexample>
</para>
<note>
<simpara>
Prior to PHP 8.0.0, where the <function>get_debug_type</function> is not
available, the <function>gettype</function> function can be used instead.
However, it doesn't use the canonical type names.
</simpara>
</note>
</sect1>
&language.types.type-system;
&language.types.null;
&language.types.boolean;
&language.types.integer;
&language.types.float;
&language.types.string;
&language.types.numeric-strings;
&language.types.array;
&language.types.object;
&language.types.enumerations;
&language.types.resource;
&language.types.callable;
&language.types.mixed;
&language.types.void;
&language.types.never;
&language.types.relative-class-types;
&language.types.value;
&language.types.iterable;
&language.types.declarations;
&language.types.type-juggling;
</chapter>
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