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PHP magic method - attribute overloading method, PHP magic attribute overloading_PHP tutorial
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Jul 12, 2016 am 08:57 AM

php magic method - attribute overloading method, php magic attribute overloading

php has a very magical method. These methods are reserved methods and are usually not used externally. Explicitly called, they start with a double underscore (__), and they are called Magic Methods. PHP officials do not recommend defining other methods starting with double underscores.

This time we introduce the attribute overloading method: 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> )

These methods are triggered when accesses inaccessible properties .

As follows: 

<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> }

Result output: 

====================== 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 =====================

Specially emphasize that these methods will only be triggered when this attribute does not exist (based on current access permissions). Therefore it is strongly recommended to use certain key values ​​for get/set processing, especially the corresponding key values ​​​​should not have access rights issues , such as a and b in the above example, which will lead to in the class The processing methods inside, outside the class, and within the subclass are different, resulting in unpredictable return values ​​during development, which can easily lead to bugs.

The empty method cannot call the attribute overloaded method. 

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

In this example, the return value of __set itself will be ignored, and __get will not be called.

In addition: property overloaded methods must be declared public, and parameters cannot be passed by reference. Static properties cannot be overloaded through these methods, and these methods cannot be declared static.

Of course, when using magic methods, it will also affect the reflection system.

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