PHP magic method - constructor and destructor, PHP magic constructor_PHP tutorial

php magic methods - constructors and destructors, php magic constructor

php has a class of very magical methods, these methods are reserved methods, usually not external When called explicitly, 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 most common magic methods: constructors and destructors.

1. Constructor (__construct)

void __construct ([ <span>mixed</span> <span>$args</span> [, $... ]] )

Constructor: A class with a constructor will call this method first every time it creates a new object, so it is very suitable to do some initialization services before using the object.

Note:

1. clone does not call the constructor

　2. If the subclass defines a constructor, the constructor of the parent class will not be called implicitly

3. The constructor parameters of the subclass are allowed to be inconsistent with the constructor parameters of the parent class

　4. If the subclass does not define a constructor, PHP will try to find the constructor of the parent class

　5. If the parent class does not define a constructor, using the parent keyword to explicitly call the parent class constructor will result in a fatal error

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span> <span>class</span><span> P{
</span><span> 4</span> 
<span> 5</span>     <span>public</span> <span>function</span><span> __construct(){
</span><span> 6</span>         <span>echo</span> <span>__CLASS__</span> . "\n"<span>;
</span><span> 7</span> <span>    }
</span><span> 8</span> 
<span> 9</span> <span>}
</span><span>10</span> 
<span>11</span> <span>class</span> C1 <span>extends</span><span> P{
</span><span>12</span> 
<span>13</span>     <span>public</span> <span>function</span><span> __construct(){
</span><span>14</span>         <span>echo</span> <span>__CLASS__</span> . "\n"<span>;
</span><span>15</span> <span>    }
</span><span>16</span> 
<span>17</span> <span>}
</span><span>18</span> 
<span>19</span> <span>class</span> C2 <span>extends</span><span> P{
</span><span>20</span> 
<span>21</span>     <span>public</span> <span>function</span><span> __construct(){
</span><span>22</span>         parent::<span>__construct();
</span><span>23</span>         <span>echo</span> <span>__CLASS__</span> . "\n"<span>;
</span><span>24</span> <span>    }
</span><span>25</span> 
<span>26</span> <span>}
</span><span>27</span> 
<span>28</span> <span>class</span> C3 <span>extends</span><span> P{
</span><span>29</span> 
<span>30</span> <span>}
</span><span>31</span> 
<span>32</span> <span>//</span><span> P</span>
<span>33</span> <span>$ins</span> = <span>new</span><span> P();
</span><span>34</span> 
<span>35</span> <span>//</span><span> Nothing</span>
<span>36</span> <span>$ins2</span> = <span>clone</span> <span>$ins</span><span>;
</span><span>37</span> 
<span>38</span> <span>//</span><span> C1</span>
<span>39</span> <span>new</span><span> C1();
</span><span>40</span> 
<span>41</span> <span>//</span><span> P
</span><span>42</span> <span>// C2</span>
<span>43</span> <span>new</span><span> C2();
</span><span>44</span> 
<span>45</span> <span>//</span><span> P</span>
<span>46</span> <span>new</span> C3();

In addition to the constructor of the magic method, PHP also supports a constructor with the same name as the class, but its priority is lower than the magic method:

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span> <span>class</span><span> C1{
</span><span> 4</span> 
<span> 5</span>     <span>public</span> <span>function</span><span> C1(){
</span><span> 6</span>         <span>echo</span> <span>__CLASS__</span> . "1\n"<span>;
</span><span> 7</span> <span>    }
</span><span> 8</span> 
<span> 9</span>     <span>public</span> <span>function</span><span> __construct(){
</span><span>10</span>         <span>echo</span> <span>__CLASS__</span> . "2\n"<span>;
</span><span>11</span> <span>    }
</span><span>12</span> 
<span>13</span> <span>}
</span><span>14</span> 
<span>15</span> <span>class</span><span> C2{
</span><span>16</span> 
<span>17</span>     <span>public</span> <span>function</span><span> C2(){
</span><span>18</span>         <span>echo</span> <span>__CLASS__</span> . "1\n"<span>;
</span><span>19</span> <span>    }
</span><span>20</span> 
<span>21</span> <span>}
</span><span>22</span> 
<span>23</span> <span>class</span><span> C3{
</span><span>24</span> 
<span>25</span>     <span>public</span> <span>function</span><span> C3(){
</span><span>26</span>         <span>echo</span> <span>__CLASS__</span> . "1\n"<span>;
</span><span>27</span> <span>    }
</span><span>28</span> 
<span>29</span>     <span>public</span> <span>function</span><span> __construct(){
</span><span>30</span>         <span>echo</span> <span>__CLASS__</span> . "2\n"<span>;
</span><span>31</span>         <span>$this</span>-><span>C3();
</span><span>32</span> <span>    }
</span><span>33</span> 
<span>34</span> <span>}
</span><span>35</span> 
<span>36</span> <span>//</span><span> C12</span>
<span>37</span> <span>new</span><span> C1();
</span><span>38</span> 
<span>39</span> <span>//</span><span> C21</span>
<span>40</span> <span>new</span><span> C2();
</span><span>41</span> 
<span>42</span> <span>//</span><span> C32
</span><span>43</span> <span>// C31</span>
<span>44</span> <span>new</span> C3();

After php5.3.3, the method with the same name as the class name is used within the namespace and is no longer used as a constructor. It remains unchanged outside the namespace:

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span> <span>namespace N;
</span><span> 4</span> 
<span> 5</span> <span>class</span><span> C{
</span><span> 6</span> 
<span> 7</span>     <span>public</span> <span>function</span><span> C(){
</span><span> 8</span>         <span>echo</span> <span>__CLASS__</span> . "\n"<span>;
</span><span> 9</span> <span>    }   
</span><span>10</span> 
<span>11</span> <span>}
</span><span>12</span> 
<span>13</span> <span>//</span><span> Nothing</span>
<span>14</span> <span>new</span> \N\C();

The constructor can use all three access control modifiers, such as singleton mode:

<span> 1</span> <?<span>php
</span><span> 2</span> 
<span> 3</span> <span>class</span><span> Single{
</span><span> 4</span> 
<span> 5</span>     <span>public</span> <span>static</span> <span>function</span><span> getInstance(){
</span><span> 6</span>         <span>static</span> <span>$ins</span> = <span>null</span><span>;
</span><span> 7</span>         <span>if</span>(<span>empty</span>(<span>$ins</span><span>)){
</span><span> 8</span>             <span>$ins</span> = <span>new</span><span> self();
</span><span> 9</span> <span>        }   
</span><span>10</span>         <span>return</span> <span>$ins</span><span>;
</span><span>11</span> <span>    }   
</span><span>12</span> 
<span>13</span>     <span>private</span> <span>function</span><span> __construct(){
</span><span>14</span>         <span>echo</span> <span>__CLASS__</span> . "\n"<span>;
</span><span>15</span> <span>    }   
</span><span>16</span> 
<span>17</span> <span>}
</span><span>18</span> 
<span>19</span> <span>//</span><span> Single</span>
<span>20</span> Single::getInstance();

2. Destructor (__destruct)

void __destruct ( void )

Destructor: The destructor will be executed when all references to an object are deleted or the object is explicitly destroyed.

Note:

　1. Similar to the constructor, the destructor of the parent class will not be called secretly by the engine and must be explicitly called parent::__destruct

2. exit and die cannot prevent the execution of the destructor

　3. Fatal errors will prevent the execution of the destructor

　4. Calling exit in the destructor can prevent the execution of other unexecuted destructors

　5. If the parent class does not define a destructor, using the parent keyword to explicitly call the parent class's destructor function will result in a fatal error

<?<span>php

</span><span>class</span><span> P{

    </span><span>function</span><span> __destruct(){
        </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>;
    }   
}

</span><span>class</span> C1 <span>extends</span><span> P{

    </span><span>function</span><span> __destruct(){
        </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>;
    }   

}

</span><span>class</span> C2 <span>extends</span><span> P{

    </span><span>function</span><span> __destruct(){
        parent</span>::<span>__destruct();
        </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>;
    }   

}

</span><span>class</span> C3 <span>extends</span><span> P{

}

</span><span>$insP</span> = <span>new</span><span> P();
</span><span>$ins1</span> = <span>new</span><span> C1();
</span><span>$ins2</span> = <span>new</span><span> C2();
</span><span>$ins3</span> = <span>new</span><span> C3();

</span><span>/*</span><span>*
输出：
C3    P
C2    P
C2    C2
C1    C1
P    P
*</span><span>*/</span>

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