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Started the OOP5 traits documentation.

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Justin Martin 2011-06-29 06:40:04 +00:00
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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 298604 $ -->
<sect1 xml:id="language.oop5.traits" xmlns="http://docbook.org/ns/docbook">
<title>Traits</title>
<para>
Traits is a mechanism for code reuse in single inheritance languages such as
PHP. A Trait is intended to reduce some limitations of single inheritance by
enabling a developer to reuse sets of methods freely in several independent
classes living in different class hierarchies. The semantics of the combination
of Traits and classes is defined in a way which reduces complexity, and avoids
the typical problems associated with multiple inheritance and Mixins.
</para>
<para>
A Trait is similar to a class, but only intended to group functionality in a
fine-grained and consistent way. It is not possible to instantiate a Trait on
its own. It is an addition to traditional inheritance and enables horizontal
composition of behavior; that is, the application of class members without
requiring inheritance.
</para>
<sect2 xml:id="language.oop5.traits.precedence">
<title>Precedence</title>
<para>
An inherited member from a base class is overridden by a member inserted
by a Trait. The precedence order is that members from the current class
override Trait methods, which in return override inherited methods.
</para>
</sect2>
<sect2 xml:id="language.oop5.traits.multiple">
<title>Multiple Traits</title>
<para>
Multiple Traits can be inserted into a class by listing them in the use
statement, separated by commas.
</para>
</sect2>
<sect2 xml:id="language.oop5.traits.conflict">
<title>Conflict Resolution</title>
<para>
If two Traits insert a member by the same name, a fatal error is produced,
if the conflict is not explicitly resolved.
</para>
<para>
To resolve conflicted naming among Traits, one can use the <literal>insteadof</literal>
operator to explicitly define the precedence between said Traits. Or,
one can use the <literal>as</literal> operator to alias the conflicting
member name(s).
</para>
</sect2>
<sect2 xml:id="language.oop5.traits.examples">
&reftitle.examples;
<example xml:id="language.oop5.traits.examples.ex1">
<title>Trait example</title>
<programlisting role="php">
<![CDATA[
<?php
trait ezcReflectionReturnInfo {
function getReturnType() { /*1*/ }
function getReturnDescription() { /*2*/ }
}
class ezcReflectionMethod extends ReflectionMethod {
use ezcReflectionReturnInfo;
/* ... */
}
class ezcReflectionFunction extends ReflectionFunction {
use ezcReflectionReturnInfo;
/* ... */
}
?>
]]>
</programlisting>
</example>
</sect2>
</sect1>
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