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Jul 12, 2016 am 08:57 AM

php魔术方法——属性重载方法，php魔术属性重载

php有一类很神奇的方法，这些方法是保留方法，通常不会在外部被显式调用，他们使用双下划线(__)开头，他们被称为魔术方法(Magic Methods)。php官方也不建议定义其他双下划线开头的方法。

这次介绍属性重载方法：get/set/isset/unset

<span>public</span> void __set ( <span>string</span> <span>$name</span> , <span>mixed</span> <span>$value</span><span> )

</span><span>public</span> <span>mixed</span> __get ( <span>string</span> <span>$name</span><span> )

</span><span>public</span> bool __isset ( <span>string</span> <span>$name</span><span> )

</span><span>public</span> void __unset ( <span>string</span> <span>$name</span> )

这些方法触发的时机，都是在访问不可访问的属性的时候。

如以下：

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span> <span>class</span><span> Cls{
</span><span> 4</span> 
<span> 5</span>     <span>private</span> <span>$a</span> = 0<span>;
</span><span> 6</span>     <span>protected</span> <span>$b</span> = 1<span>;
</span><span> 7</span>     <span>public</span> <span>$c</span> = 2<span>;
</span><span> 8</span>     <span>var</span> <span>$d</span> = 3<span>;
</span><span> 9</span> 
<span>10</span>     <span>private</span> <span>$_properties</span> = <span>array</span>(0<span>);
</span><span>11</span> 
<span>12</span>     <span>public</span> <span>function</span> __set(<span>$name</span>, <span>$value</span><span>){
</span><span>13</span>         <span>echo</span> <span>__METHOD__</span> . ' is called! ' . json_encode(<span>func_get_args</span>()) . "\n"<span>;
</span><span>14</span>         <span>return</span> <span>$this</span>->_properties[<span>$name</span>] = <span>$value</span><span>;
</span><span>15</span> <span>    }
</span><span>16</span> 
<span>17</span>     <span>public</span> <span>function</span> __get(<span>$name</span><span>){
</span><span>18</span>         <span>echo</span> <span>__METHOD__</span> . ' is called! ' . json_encode(<span>func_get_args</span>()) . "\n"<span>;
</span><span>19</span>         <span>return</span> <span>$this</span>->_properties[<span>$name</span><span>];
</span><span>20</span> <span>    }
</span><span>21</span> 
<span>22</span>     <span>public</span> <span>function</span> __isset(<span>$name</span><span>){
</span><span>23</span>         <span>echo</span> <span>__METHOD__</span> . ' is called! ' . json_encode(<span>func_get_args</span>()) . "\n"<span>;
</span><span>24</span>         <span>return</span> <span>isset</span>(<span>$this</span>->_properties[<span>$name</span><span>]);
</span><span>25</span> <span>    }
</span><span>26</span> 
<span>27</span>     <span>public</span> <span>function</span> __unset(<span>$name</span><span>){
</span><span>28</span>         <span>echo</span> <span>__METHOD__</span> . ' is called! ' . json_encode(<span>func_get_args</span>()) . "\n"<span>;
</span><span>29</span>         <span>unset</span>(<span>$this</span>->_properties[<span>$name</span><span>]);
</span><span>30</span> <span>    }
</span><span>31</span> 
<span>32</span>     <span>public</span> <span>function</span><span> dump(){
</span><span>33</span>         <span>echo</span> "====================== DUMP START ====================\n"<span>;
</span><span>34</span>         <span>echo</span> <<<<span>STR
</span><span>35</span>     a: <span>$this</span>-><span>a
</span><span>36</span>     b: <span>$this</span>-><span>b
</span><span>37</span>     c: <span>$this</span>-><span>c
</span><span>38</span>     d: <span>$this</span>-><span>d\n
</span><span>39</span> <span>STR;
</span><span>40</span>         <span>foreach</span>(<span>$this</span>->_properties <span>as</span> <span>$k</span> => <span>$v</span><span>){
</span><span>41</span>             <span>echo</span> <<<<span>STR
</span><span>42</span>     Property <span>$k</span>: <span>$v</span><span>\n
</span><span>43</span> <span>STR;
</span><span>44</span> <span>        }
</span><span>45</span>     
<span>46</span>         <span>echo</span> "====================== DUMP STOP =====================\n"<span>;
</span><span>47</span>         
<span>48</span> <span>    }
</span><span>49</span> <span>}
</span><span>50</span> <span>$string</span> = 'abcdef'<span>;
</span><span>51</span> <span>$obj</span> = <span>new</span><span> Cls();
</span><span>52</span> 
<span>53</span> <span>$list</span> = <span>array</span>('isset', 'get', 'set', 'isset', 'unset', 'isset'<span>);
</span><span>54</span> <span>$obj</span>-><span>dump();
</span><span>55</span> <span>foreach</span>(<span>$list</span> <span>as</span> <span>$method</span><span>){
</span><span>56</span>     <span>for</span>(<span>$i</span> = 0 ; <span>$i</span> < <span>strlen</span>(<span>$string</span>) ; <span>$i</span> ++<span>){
</span><span>57</span>         <span>$char</span> = <span>$string</span>{<span>$i</span><span>};
</span><span>58</span>         <span>echo</span> "------ <span>$method</span> : <span>$char</span> ------\n"<span>;
</span><span>59</span>         <span>switch</span>(<span>$method</span><span>){
</span><span>60</span>             <span>case</span> 'isset':
<span>61</span>                 <span>echo</span> json_encode(<span>$tmp</span> = <span>isset</span>(<span>$obj</span>-><span>$char</span>)) . "\n"<span>;
</span><span>62</span>                 <span>break</span><span>;
</span><span>63</span>             <span>case</span> 'get':
<span>64</span>                 <span>echo</span> json_encode(<span>$tmp</span> = <span>$obj</span>-><span>$char</span>) . "\n"<span>;
</span><span>65</span>                 <span>break</span><span>;
</span><span>66</span>             <span>case</span> 'set':
<span>67</span>                 <span>echo</span> json_encode(<span>$tmp</span> = <span>$obj</span>-><span>$char</span> = <span>$char</span> . "-val") . "\n"<span>;
</span><span>68</span>                 <span>break</span><span>;
</span><span>69</span>             <span>case</span> 'unset':
<span>70</span>                 <span>unset</span>(<span>$obj</span>-><span>$char</span><span>);
</span><span>71</span>                 <span>break</span><span>;
</span><span>72</span>             <span>default</span>:
<span>73</span>                 <span>break</span><span>;
</span><span>74</span> <span>        }
</span><span>75</span> <span>    }
</span><span>76</span>     <span>$obj</span>-><span>dump();
</span><span>77</span> }

结果输出：

====================== DUMP START ====================<span>
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>: 2<span>
    d</span>: 3<span>
    Property </span>0: 0
====================== DUMP STOP =====================
------ <span>isset</span> : a ------<span>
Cls</span>::__isset is called! ["a"<span>]
</span><span>false</span>
------ <span>isset</span> : b ------<span>
Cls</span>::__isset is called! ["b"<span>]
</span><span>false</span>
------ <span>isset</span> : c ------
<span>true</span>
------ <span>isset</span> : d ------
<span>true</span>
------ <span>isset</span> : e ------<span>
Cls</span>::__isset is called! ["e"<span>]
</span><span>false</span>
------ <span>isset</span> : f ------<span>
Cls</span>::__isset is called! ["f"<span>]
</span><span>false</span>
====================== DUMP START ====================<span>
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>: 2<span>
    d</span>: 3<span>
    Property </span>0: 0
====================== DUMP STOP =====================
------ get : a ------<span>
Cls</span>::__get is called! ["a"<span>]
</span><span>null</span>
------ get : b ------<span>
Cls</span>::__get is called! ["b"<span>]
</span><span>null</span>
------ get : c ------
2
------ get : d ------
3
------ get : e ------<span>
Cls</span>::__get is called! ["e"<span>]
</span><span>null</span>
------ get : f ------<span>
Cls</span>::__get is called! ["f"<span>]
</span><span>null</span>
====================== DUMP START ====================<span>
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>: 2<span>
    d</span>: 3<span>
    Property </span>0: 0
====================== DUMP STOP =====================
------ set : a ------<span>
Cls</span>::__set is called! ["a","a-val"<span>]
</span>"a-val"
------ set : b ------<span>
Cls</span>::__set is called! ["b","b-val"<span>]
</span>"b-val"
------ set : c ------
"c-val"
------ set : d ------
"d-val"
------ set : e ------<span>
Cls</span>::__set is called! ["e","e-val"<span>]
</span>"e-val"
------ set : f ------<span>
Cls</span>::__set is called! ["f","f-val"<span>]
</span>"f-val"
====================== DUMP START ====================<span>
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>: c-<span>val
    d</span>: d-<span>val
    Property </span>0: 0<span>
    Property a</span>: a-<span>val
    Property b</span>: b-<span>val
    Property e</span>: e-<span>val
    Property f</span>: f-<span>val
</span>====================== DUMP STOP =====================
------ <span>isset</span> : a ------<span>
Cls</span>::__isset is called! ["a"<span>]
</span><span>true</span>
------ <span>isset</span> : b ------<span>
Cls</span>::__isset is called! ["b"<span>]
</span><span>true</span>
------ <span>isset</span> : c ------
<span>true</span>
------ <span>isset</span> : d ------
<span>true</span>
------ <span>isset</span> : e ------<span>
Cls</span>::__isset is called! ["e"<span>]
</span><span>true</span>
------ <span>isset</span> : f ------<span>
Cls</span>::__isset is called! ["f"<span>]
</span><span>true</span>
====================== DUMP START ====================<span>
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>: c-<span>val
    d</span>: d-<span>val
    Property </span>0: 0<span>
    Property a</span>: a-<span>val
    Property b</span>: b-<span>val
    Property e</span>: e-<span>val
    Property f</span>: f-<span>val
</span>====================== DUMP STOP =====================
------ <span>unset</span> : a ------<span>
Cls</span>::__unset is called! ["a"<span>]
</span>------ <span>unset</span> : b ------<span>
Cls</span>::__unset is called! ["b"<span>]
</span>------ <span>unset</span> : c ------
------ <span>unset</span> : d ------
------ <span>unset</span> : e ------<span>
Cls</span>::__unset is called! ["e"<span>]
</span>------ <span>unset</span> : f ------<span>
Cls</span>::__unset is called! ["f"<span>]
</span>====================== DUMP START ====================<span>
Cls</span>::__get is called! ["c"<span>]
Cls</span>::__get is called! ["d"<span>]
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>:<span> 
    d</span>:<span> 
    Property </span>0: 0
====================== DUMP STOP =====================
------ <span>isset</span> : a ------<span>
Cls</span>::__isset is called! ["a"<span>]
</span><span>false</span>
------ <span>isset</span> : b ------<span>
Cls</span>::__isset is called! ["b"<span>]
</span><span>false</span>
------ <span>isset</span> : c ------<span>
Cls</span>::__isset is called! ["c"<span>]
</span><span>false</span>
------ <span>isset</span> : d ------<span>
Cls</span>::__isset is called! ["d"<span>]
</span><span>false</span>
------ <span>isset</span> : e ------<span>
Cls</span>::__isset is called! ["e"<span>]
</span><span>false</span>
------ <span>isset</span> : f ------<span>
Cls</span>::__isset is called! ["f"<span>]
</span><span>false</span>
====================== DUMP START ====================<span>
Cls</span>::__get is called! ["c"<span>]
Cls</span>::__get is called! ["d"<span>]
    a</span>: 0<span>
    b</span>: 1<span>
    c</span>:<span> 
    d</span>:<span> 
    Property </span>0: 0
====================== DUMP STOP =====================

特别强调，当这个属性不存在(基于当前访问权限)的时候，才会触发这些方法。因此严重建议使用确定的键值进行get/set处理，特别是对应的键值不要有访问权限问题，如上例中的a和b，会导致在类内部、类外部、子类内处理的方式不同，开发时产生不可预知的返回值，极易产生bug。

empty方法不能调用属性重载方法。

<span>$tmp</span> = <span>$obj</span>-><span>$char</span> = <span>$char</span> . "-val"

此例中，__set自身的返回值将被忽略，同样__get也不会被调用。

此外：属性重载方法必须声明为public，同时参数不能使用引用传递，静态属性不能通过这些方法重载，这些方法也不能被声明为static。

当然，使用魔术方法的时候，也会对反射系统造成影响。

 

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