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>章 19. 类与对象（PHP 5）</TD
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><H1
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><A
NAME="language.oop5.overloading"
>Overloading</A
></H1
><P
> Both method calls and member accesses can be overloaded via the
__call, __get and __set methods. These methods will only be
triggered when your object or inherited object doesn't contain the
member or method you're trying to access.
All overloading methods must not be defined as
<A
HREF="language.oop5.static.html"
>static</A
>.
All overloading methods must be defined as
<A
HREF="language.oop5.visibility.html"
>public</A
>.
</P
><P
> Since PHP 5.1.0 it is also possible to overload the
<A
HREF="function.isset.html"
><B
CLASS="function"
>isset()</B
></A
> and <A
HREF="function.unset.html"
><B
CLASS="function"
>unset()</B
></A
> functions via the
__isset and __unset methods respectively.
Method __isset is called also with <A
HREF="function.empty.html"
><B
CLASS="function"
>empty()</B
></A
>.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.oop5.overloading.members"
>Member overloading</A
></H2
>void <B
CLASS="methodname"
>__set</B
> ( string name, mixed value )<BR
></BR
>mixed <B
CLASS="methodname"
>__get</B
> ( string name )<BR
></BR
>bool <B
CLASS="methodname"
>__isset</B
> ( string name )<BR
></BR
>void <B
CLASS="methodname"
>__unset</B
> ( string name )<BR
></BR
><P
> Class members can be overloaded to run custom code defined in your class
by defining these specially named methods. The <CODE
CLASS="varname"
>$name</CODE
>
parameter used is the name of the variable that should be set or retrieved.
The __set() method's <CODE
CLASS="varname"
>$value</CODE
> parameter specifies the
value that the object should set the <CODE
CLASS="varname"
>$name</CODE
>.
</P
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><DIV
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><A
NAME="AEN5928"
></A
><P
><B
>例 19-20. overloading with __get, __set, __isset and __unset example</B
></P
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><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Setter<br /></font><font color="#007700">{<br /> </font><font color="#0000BB">public $n</font><font color="#007700">;<br /> </font><font color="#0000BB">private $x </font><font color="#007700">= array(</font><font color="#DD0000">"a" </font><font color="#007700">=> </font><font color="#0000BB">1</font><font color="#007700">, </font><font color="#DD0000">"b" </font><font color="#007700">=> </font><font color="#0000BB">2</font><font color="#007700">, </font><font color="#DD0000">"c" </font><font color="#007700">=> </font><font color="#0000BB">3</font><font color="#007700">);<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__get</font><font color="#007700">(</font><font color="#0000BB">$nm</font><font color="#007700">)<br /> {<br /> echo </font><font color="#DD0000">"Getting </font><font color="#007700">[</font><font color="#DD0000">$nm</font><font color="#007700">]\n</font><font color="#DD0000">"</font><font color="#007700">;<br /><br /> if (isset(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">])) {<br /> </font><font color="#0000BB">$r </font><font color="#007700">= </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">];<br /> print </font><font color="#DD0000">"Returning: $r</font><font color="#007700">\n</font><font color="#DD0000">"</font><font color="#007700">;<br /> return </font><font color="#0000BB">$r</font><font color="#007700">;<br /> } else {<br /> echo </font><font color="#DD0000">"Nothing!\n"</font><font color="#007700">;<br /> }<br /> }<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__set</font><font color="#007700">(</font><font color="#0000BB">$nm</font><font color="#007700">, </font><font color="#0000BB">$val</font><font color="#007700">)<br /> {<br /> echo </font><font color="#DD0000">"Setting </font><font color="#007700">[</font><font color="#DD0000">$nm</font><font color="#007700">]</font><font color="#DD0000"> to $val</font><font color="#007700">\n</font><font color="#DD0000">"</font><font color="#007700">;<br /><br /> if (isset(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">])) {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">] = </font><font color="#0000BB">$val</font><font color="#007700">;<br /> echo </font><font color="#DD0000">"OK!\n"</font><font color="#007700">;<br /> } else {<br /> echo </font><font color="#DD0000">"Not OK!\n"</font><font color="#007700">;<br /> }<br /> }<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__isset</font><font color="#007700">(</font><font color="#0000BB">$nm</font><font color="#007700">)<br /> {<br /> echo </font><font color="#DD0000">"Checking if $nm is set</font><font color="#007700">\n</font><font color="#DD0000">"</font><font color="#007700">;<br /><br /> return isset(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">]);<br /> }<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__unset</font><font color="#007700">(</font><font color="#0000BB">$nm</font><font color="#007700">)<br /> {<br /> echo </font><font color="#DD0000">"Unsetting $nm</font><font color="#007700">\n</font><font color="#DD0000">"</font><font color="#007700">;<br /><br /> unset(</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">[</font><font color="#0000BB">$nm</font><font color="#007700">]);<br /> }<br />}<br /><br /></font><font color="#0000BB">$foo </font><font color="#007700">= new </font><font color="#0000BB">Setter</font><font color="#007700">();<br /></font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">n </font><font color="#007700">= </font><font color="#0000BB">1</font><font color="#007700">;<br /></font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">a </font><font color="#007700">= </font><font color="#0000BB">100</font><font color="#007700">;<br /></font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">a</font><font color="#007700">++;<br /></font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">z</font><font color="#007700">++;<br /><br /></font><font color="#0000BB">var_dump</font><font color="#007700">(isset(</font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">a</font><font color="#007700">)); </font><font color="#FF8000">//true<br /></font><font color="#007700">unset(</font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">a</font><font color="#007700">);<br /></font><font color="#0000BB">var_dump</font><font color="#007700">(isset(</font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">a</font><font color="#007700">)); </font><font color="#FF8000">//false<br /><br />// this doesn't pass through the __isset() method<br />// because 'n' is a public property<br /></font><font color="#0000BB">var_dump</font><font color="#007700">(isset(</font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">n</font><font color="#007700">));<br /><br /></font><font color="#0000BB">var_dump</font><font color="#007700">(</font><font color="#0000BB">$foo</font><font color="#007700">);<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
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><TR
><TD
><code><font color="#000000">
Setting [a] to 100<br />OK!<br />Getting [a]<br />Returning: 100<br />Setting [a] to 101<br />OK!<br />Getting [z]<br />Nothing!<br />Setting [z] to 1<br />Not OK!<br /><br />Checking if a is set<br />bool(true)<br />Unsetting a<br />Checking if a is set<br />bool(false)<br />bool(true)<br /><br />object(Setter)#1 (2) {<br /> ["n"]=><br /> int(1)<br /> ["x:private"]=><br /> array(2) {<br /> ["b"]=><br /> int(2)<br /> ["c"]=><br /> int(3)<br /> }<br />}</font>
</code></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.oop5.overloading.methods"
>Method overloading</A
></H2
>mixed <B
CLASS="methodname"
>__call</B
> ( string name, array arguments )<BR
></BR
><P
> The magic method __call() allows to capture invocation of non existing
methods. That way __call() can be used to implement user defined method
handling that depends on the name of the actual method being called. This
is for instance useful for proxy implementations. The arguments that were
passed in the function will be defined as an array in the
<CODE
CLASS="varname"
>$arguments</CODE
> parameter. The value returned from the
__call() method will be returned to the caller of the method.
</P
><TABLE
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><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN5946"
></A
><P
><B
>例 19-21. overloading with __call example</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">Caller<br /></font><font color="#007700">{<br /> </font><font color="#0000BB">private $x </font><font color="#007700">= array(</font><font color="#0000BB">1</font><font color="#007700">, </font><font color="#0000BB">2</font><font color="#007700">, </font><font color="#0000BB">3</font><font color="#007700">);<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">__call</font><font color="#007700">(</font><font color="#0000BB">$m</font><font color="#007700">, </font><font color="#0000BB">$a</font><font color="#007700">)<br /> {<br /> print </font><font color="#DD0000">"Method $m called:</font><font color="#007700">\n</font><font color="#DD0000">"</font><font color="#007700">;<br /> </font><font color="#0000BB">var_dump</font><font color="#007700">(</font><font color="#0000BB">$a</font><font color="#007700">);<br /> return </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">x</font><font color="#007700">;<br /> }<br />}<br /><br /></font><font color="#0000BB">$foo </font><font color="#007700">= new </font><font color="#0000BB">Caller</font><font color="#007700">();<br /></font><font color="#0000BB">$a </font><font color="#007700">= </font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">test</font><font color="#007700">(</font><font color="#0000BB">1</font><font color="#007700">, </font><font color="#DD0000">"2"</font><font color="#007700">, </font><font color="#0000BB">3.4</font><font color="#007700">, </font><font color="#0000BB">true</font><font color="#007700">);<br /></font><font color="#0000BB">var_dump</font><font color="#007700">(</font><font color="#0000BB">$a</font><font color="#007700">);<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
Method test called:<br />array(4) {<br /> [0]=><br /> int(1)<br /> [1]=><br /> string(1) "2"<br /> [2]=><br /> float(3.4)<br /> [3]=><br /> bool(true)<br />}<br />array(3) {<br /> [0]=><br /> int(1)<br /> [1]=><br /> int(2)<br /> [2]=><br /> int(3)<br />}</font>
</code></TD
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