types.xml

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<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>.
  </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.literal;
 &language.types.iterable;
 &language.types.declarations;
 &language.types.type-juggling;

</chapter>
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