php魔术方法——构造函数和析构函数,php魔术构造函数
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。
这次介绍最常见的魔术方法:构造函数和析构函数。
1. 构造函数(__construct)
void __construct ([ <span>mixed</span> <span>$args</span> [, $... ]] )
构造函数:拥有构造函数的类会在每次创建新对象时先调用此方法,所以非常适合在使用对象前做一些初始化服务。
注意:
1. clone并不会调用构造函数
2. 如果子类定义了构造函数,则不会隐式调用父类的构造函数
3. 子类的构造函数允许和父类的构造函数参数不一致
4. 如果子类没有定义构造函数,php会尝试寻找父类的构造函数
5. 如果父类没有定义构造函数,使用parent关键字显式调用父类构造函数,会导致致命错误
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>class</span><span> P{ </span><span> 4</span> <span> 5</span> <span>public</span> <span>function</span><span> __construct(){ </span><span> 6</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span> 7</span> <span> } </span><span> 8</span> <span> 9</span> <span>} </span><span>10</span> <span>11</span> <span>class</span> C1 <span>extends</span><span> P{ </span><span>12</span> <span>13</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>14</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>15</span> <span> } </span><span>16</span> <span>17</span> <span>} </span><span>18</span> <span>19</span> <span>class</span> C2 <span>extends</span><span> P{ </span><span>20</span> <span>21</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>22</span> parent::<span>__construct(); </span><span>23</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>24</span> <span> } </span><span>25</span> <span>26</span> <span>} </span><span>27</span> <span>28</span> <span>class</span> C3 <span>extends</span><span> P{ </span><span>29</span> <span>30</span> <span>} </span><span>31</span> <span>32</span> <span>//</span><span> P</span> <span>33</span> <span>$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();
除了魔术方法的构造函数,php还支持与类名相同的构造函数,不过优先级比魔术方法低:
<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>$this</span>-><span>C3(); </span><span>32</span> <span> } </span><span>33</span> <span>34</span> <span>} </span><span>35</span> <span>36</span> <span>//</span><span> C12</span> <span>37</span> <span>new</span><span> C1(); </span><span>38</span> <span>39</span> <span>//</span><span> C21</span> <span>40</span> <span>new</span><span> C2(); </span><span>41</span> <span>42</span> <span>//</span><span> C32 </span><span>43</span> <span>// C31</span> <span>44</span> <span>new</span> C3();
php5.3.3之后,在命名空间之内使用与类名同名的方法,不再作为构造函数,命名空间之外不变:
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>namespace N; </span><span> 4</span> <span> 5</span> <span>class</span><span> C{ </span><span> 6</span> <span> 7</span> <span>public</span> <span>function</span><span> C(){ </span><span> 8</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span> 9</span> <span> } </span><span>10</span> <span>11</span> <span>} </span><span>12</span> <span>13</span> <span>//</span><span> Nothing</span> <span>14</span> <span>new</span> \N\C();
构造函数可以用全部三个访问控制修饰符,如单例模式:
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>class</span><span> Single{ </span><span> 4</span> <span> 5</span> <span>public</span> <span>static</span> <span>function</span><span> getInstance(){ </span><span> 6</span> <span>static</span> <span>$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>$ins</span><span>; </span><span>11</span> <span> } </span><span>12</span> <span>13</span> <span>private</span> <span>function</span><span> __construct(){ </span><span>14</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>15</span> <span> } </span><span>16</span> <span>17</span> <span>} </span><span>18</span> <span>19</span> <span>//</span><span> Single</span> <span>20</span> Single::getInstance();
2. 析构函数(__destruct)
void __destruct ( void )
析构函数:析构函数会在某个对象的引用被全部删除或对象被显示销毁时执行。
注意:
1. 同构造函数类似,父类的析构函数并不会被引擎暗中调用,必须显式调用parent::__destruct
2. exit和die并不能阻止析构函数的执行
3. 致命错误会阻止析构函数的执行
4. 在析构函数中调用exit,可以阻止其他未执行的析构函数的执行
5. 如果父类没有定义析构函数,使用parent关键字显式调用父类析构函数,会导致致命错误
<?<span>php </span><span>class</span><span> P{ </span><span>function</span><span> __destruct(){ </span><span>echo</span> <span>get_class</span>(<span>$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>

PHP仍然流行的原因是其易用性、灵活性和强大的生态系统。1)易用性和简单语法使其成为初学者的首选。2)与web开发紧密结合,处理HTTP请求和数据库交互出色。3)庞大的生态系统提供了丰富的工具和库。4)活跃的社区和开源性质使其适应新需求和技术趋势。

PHP和Python都是高层次的编程语言,广泛应用于Web开发、数据处理和自动化任务。1.PHP常用于构建动态网站和内容管理系统,而Python常用于构建Web框架和数据科学。2.PHP使用echo输出内容,Python使用print。3.两者都支持面向对象编程,但语法和关键字不同。4.PHP支持弱类型转换,Python则更严格。5.PHP性能优化包括使用OPcache和异步编程,Python则使用cProfile和异步编程。

PHP主要是过程式编程,但也支持面向对象编程(OOP);Python支持多种范式,包括OOP、函数式和过程式编程。PHP适合web开发,Python适用于多种应用,如数据分析和机器学习。

PHP起源于1994年,由RasmusLerdorf开发,最初用于跟踪网站访问者,逐渐演变为服务器端脚本语言,广泛应用于网页开发。Python由GuidovanRossum于1980年代末开发,1991年首次发布,强调代码可读性和简洁性,适用于科学计算、数据分析等领域。

PHP适合网页开发和快速原型开发,Python适用于数据科学和机器学习。1.PHP用于动态网页开发,语法简单,适合快速开发。2.Python语法简洁,适用于多领域,库生态系统强大。

PHP在现代化进程中仍然重要,因为它支持大量网站和应用,并通过框架适应开发需求。1.PHP7提升了性能并引入了新功能。2.现代框架如Laravel、Symfony和CodeIgniter简化开发,提高代码质量。3.性能优化和最佳实践进一步提升应用效率。

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP类型提示提升代码质量和可读性。1)标量类型提示:自PHP7.0起,允许在函数参数中指定基本数据类型,如int、float等。2)返回类型提示:确保函数返回值类型的一致性。3)联合类型提示:自PHP8.0起,允许在函数参数或返回值中指定多个类型。4)可空类型提示:允许包含null值,处理可能返回空值的函数。


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