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>章 19. 类与对象（PHP 5）</TD
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CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="language.oop5.magic"
>Magic Methods</A
></H1
><P
> The function names
<TT
CLASS="literal"
>__construct</TT
>,
<TT
CLASS="literal"
>__destruct</TT
>
(see <A
HREF="language.oop5.decon.html"
>Constructors and Destructors</A
>),
<TT
CLASS="literal"
>__call</TT
>,
<TT
CLASS="literal"
>__get</TT
>,
<TT
CLASS="literal"
>__set</TT
>,
<TT
CLASS="literal"
>__isset</TT
>,
<TT
CLASS="literal"
>__unset</TT
>
(see <A
HREF="language.oop5.overloading.html"
>Overloading</A
>),
<TT
CLASS="literal"
>__sleep</TT
>,
<TT
CLASS="literal"
>__wakeup</TT
>,
<TT
CLASS="literal"
>__toString</TT
>,
<TT
CLASS="literal"
>__set_state</TT
>,
<A
HREF="language.oop5.cloning.html"
>__clone</A
> and
<A
HREF="language.oop5.autoload.html"
>__autoload</A
>
are magical in PHP classes. You
cannot have functions with these names in any of your
classes unless you want the magic functionality associated
with them.
</P
><DIV
CLASS="caution"
><P
></P
><TABLE
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><TR
><TD
ALIGN="CENTER"
><B
>小心</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> PHP reserves all function names starting with __ as magical.
It is recommended that you do not use function names with
__ in PHP unless you want some documented magic functionality.
</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.oop5.magic.sleep"
><TT
CLASS="literal"
>__sleep</TT
> and <TT
CLASS="literal"
>__wakeup</TT
></A
></H2
><P
> <A
HREF="function.serialize.html"
><B
CLASS="function"
>serialize()</B
></A
> checks if your class has a function with
the magic name <TT
CLASS="literal"
>__sleep</TT
>. If so, that function is
executed prior to any serialization. It can clean up the object
and is supposed to return an array with the names of all variables
of that object that should be serialized.
If the method doesn't return anything then <TT
CLASS="constant"
><B
>NULL</B
></TT
> is serialized and
E_NOTICE is issued.
</P
><P
> The intended use of <TT
CLASS="literal"
>__sleep</TT
> is to commit pending
data or perform similar cleanup tasks. Also, the function is
useful if you have very large objects which do not need to be
saved completely.
</P
><P
> The <TT
CLASS="literal"
>__sleep</TT
> method should return the value to serialize
(usually <TT
CLASS="literal"
>$this</TT
>), otherwise <TT
CLASS="constant"
><B
>NULL</B
></TT
> is serialized.
</P
><P
> Conversely, <A
HREF="function.unserialize.html"
><B
CLASS="function"
>unserialize()</B
></A
> checks for the
presence of a function with the magic name
<TT
CLASS="literal"
>__wakeup</TT
>. If present, this function can
reconstruct any resources that the object may have.
</P
><P
> The intended use of <TT
CLASS="literal"
>__wakeup</TT
> is to
reestablish any database connections that may have been lost
during serialization and perform other reinitialization
tasks.
</P
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN6045"
></A
><P
><B
>例 19-27. Sleep and wakeup</B
></P
><TABLE
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><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Connection </font><font color="#007700">{<br /> </font><font color="#0000BB">protected $link</font><font color="#007700">;<br /> </font><font color="#0000BB">private $server</font><font color="#007700">, </font><font color="#0000BB">$username</font><font color="#007700">, </font><font color="#0000BB">$password</font><font color="#007700">, </font><font color="#0000BB">$db</font><font color="#007700">;<br /> <br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__construct</font><font color="#007700">(</font><font color="#0000BB">$server</font><font color="#007700">, </font><font color="#0000BB">$username</font><font color="#007700">, </font><font color="#0000BB">$password</font><font color="#007700">, </font><font color="#0000BB">$db</font><font color="#007700">)<br /> {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">server </font><font color="#007700">= </font><font color="#0000BB">$server</font><font color="#007700">;<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">username </font><font color="#007700">= </font><font color="#0000BB">$username</font><font color="#007700">;<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">password </font><font color="#007700">= </font><font color="#0000BB">$password</font><font color="#007700">;<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">db </font><font color="#007700">= </font><font color="#0000BB">$db</font><font color="#007700">;<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">connect</font><font color="#007700">();<br /> }<br /> <br /> </font><font color="#0000BB">private </font><font color="#007700">function </font><font color="#0000BB">connect</font><font color="#007700">()<br /> {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">link </font><font color="#007700">= </font><font color="#0000BB">mysql_connect</font><font color="#007700">(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">server</font><font color="#007700">, </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">username</font><font color="#007700">, </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">password</font><font color="#007700">);<br /> </font><font color="#0000BB">mysql_select_db</font><font color="#007700">(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">db</font><font color="#007700">, </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">link</font><font color="#007700">);<br /> }<br /> <br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__sleep</font><font color="#007700">()<br /> {<br /> return array(</font><font color="#DD0000">'server'</font><font color="#007700">, </font><font color="#DD0000">'username'</font><font color="#007700">, </font><font color="#DD0000">'password'</font><font color="#007700">, </font><font color="#DD0000">'db'</font><font color="#007700">);<br /> }<br /> <br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__wakeup</font><font color="#007700">()<br /> {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">connect</font><font color="#007700">();<br /> }<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.oop5.magic.tostring"
><TT
CLASS="literal"
>__toString</TT
></A
></H2
><P
> The <TT
CLASS="literal"
>__toString</TT
> method allows a class to decide
how it will react when it is converted to a string.
</P
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN6053"
></A
><P
><B
>例 19-28. Simple example</B
></P
><TABLE
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><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#FF8000">// Declare a simple class<br /></font><font color="#007700">class </font><font color="#0000BB">TestClass<br /></font><font color="#007700">{<br /> </font><font color="#0000BB">public $foo</font><font color="#007700">;<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__construct</font><font color="#007700">(</font><font color="#0000BB">$foo</font><font color="#007700">) {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">foo </font><font color="#007700">= </font><font color="#0000BB">$foo</font><font color="#007700">;<br /> }<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__toString</font><font color="#007700">() {<br /> return </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">foo</font><font color="#007700">;<br /> }<br />}<br /><br /></font><font color="#0000BB">$class </font><font color="#007700">= new </font><font color="#0000BB">TestClass</font><font color="#007700">(</font><font color="#DD0000">'Hello'</font><font color="#007700">);<br />echo </font><font color="#0000BB">$class</font><font color="#007700">;<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
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><TR
><TD
><PRE
CLASS="screen"
>Hello</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
><P
> It is worth noting that before PHP 5.2.0 the <TT
CLASS="literal"
>__toString</TT
>
method was only called when it was directly combined with
<A
HREF="function.echo.html"
><B
CLASS="function"
>echo()</B
></A
> or <A
HREF="function.print.html"
><B
CLASS="function"
>print()</B
></A
>.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.oop5.magic.set-state"
><TT
CLASS="literal"
>__set_state</TT
></A
></H2
><P
> This <A
HREF="language.oop5.static.html"
>static</A
> method is called
for classes exported by <A
HREF="function.var-export.html"
><B
CLASS="function"
>var_export()</B
></A
> since PHP 5.1.0.
</P
><P
> The only parameter of this method is an array containing exported
properties in the form <TT
CLASS="literal"
>array('property' => value, ...)</TT
>.
</P
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