PHP之Trait详解

你的名字 2022-09-03 15:13 171阅读 0赞

> php从以前到现在一直都是单继承的语言，无法同时从两个基类中继承属性和方法，为了解决这个问题，php出了Trait这个特性

用法：通过在类中使用use 关键字，声明要组合的Trait名称，具体的Trait的声明使用Trait关键词，Trait不能实例化

如下代码实例:

<?php
 trait Dog{ 
 public $name="dog";
 public function bark(){ 
 echo "This is dog";
 }
 }
 class Animal{ 
 public function eat(){ 
 echo "This is animal eat";
 }
 }
 class Cat extends Animal{ 
 use Dog;
 public function drive(){ 
 echo "This is cat drive";
 }
 }
 $cat = new Cat();
 $cat->drive();
 echo " ";
 $cat->eat();
 echo " ";
 $cat->bark();
 ?>

将会如下输出  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjA2NDAw_size_16_color_FFFFFF_t_70]

## 再测试Trait、基类和本类对同名属性或方法的处理，如下代码 ##

<?php
 trait Dog{ 
 public $name="dog";
 public function drive(){ 
 echo "This is dog drive";
 }
 public function eat(){ 
 echo "This is dog eat";
 }
 }
 
 class Animal{ 
 public function drive(){ 
 echo "This is animal drive";
 }
 public function eat(){ 
 echo "This is animal eat";
 }
 }
 
 class Cat extends Animal{ 
 use Dog;
 public function drive(){ 
 echo "This is cat drive";
 }
 }
 $cat = new Cat();
 $cat->drive();
 echo " ";
 $cat->eat();
 
 ?>

如下显示  
![在这里插入图片描述][489b5a2e1f714d54a62041101a433cc7.png]  
所以：Trait中的方法会覆盖 基类中的同名方法，而本类会覆盖Trait中同名方法  
注意点：当trait定义了属性后，类就不能定义同样名称的属性，否则会产生 fatal error，除非是设置成相同可见度、相同默认值。不过在php7之前，即使这样设置，还是会产生E\_STRICT 的提醒

## 一个类可以组合多个Trait，通过逗号相隔，如下 ##

use trait1,trait2

当不同的trait中，却有着同名的方法或属性，会产生冲突，可以使用insteadof或 as进行解决，insteadof 是进行替代，而as是给它取别名  
如下实例：

<?php
 trait trait1{ 
 public function eat(){ 
 echo "This is trait1 eat";
 }
 public function drive(){ 
 echo "This is trait1 drive";
 }
 }
 trait trait2{ 
 public function eat(){ 
 echo "This is trait2 eat";
 }
 public function drive(){ 
 echo "This is trait2 drive";
 }
 }
 class cat{ 
 use trait1,trait2{ 
 trait1::eat insteadof trait2;
 trait1::drive insteadof trait2;
 }
 }
 class dog{ 
 use trait1,trait2{ 
 trait1::eat insteadof trait2;
 trait1::drive insteadof trait2;
 trait2::eat as eaten;
 trait2::drive as driven;
 }
 }
 $cat = new cat();
 $cat->eat();
 echo " ";
 $cat->drive();
 echo " ";
 echo " ";
 echo " ";
 $dog = new dog();
 $dog->eat();
 echo " ";
 $dog->drive();
 echo " ";
 $dog->eaten();
 echo " ";
 $dog->driven();
 ?>

输出如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjA2NDAw_size_16_color_FFFFFF_t_70 1]

as 还可以修改方法的访问控制

<?php
 trait Animal{ 
 public function eat(){ 
 echo "This is Animal eat";
 }
 }
 
 class Dog{ 
 use Animal{ 
 eat as protected;
 }
 }
 class Cat{ 
 use Animal{ 
 Animal::eat as private eaten;
 }
 }
 $dog = new Dog();
 $dog->eat();//报错，因为已经把eat改成了保护
 
 $cat = new Cat();
 $cat->eat();//正常运行，不会修改原先的访问控制
 $cat->eaten();//报错，已经改成了私有的访问控制
 ?>

## Trait也可以互相组合，还可以使用抽象方法，静态属性，静态方法等，实例如下 ##

<?php
 trait Cat{ 
 public function eat(){ 
 echo "This is Cat eat";
 }
 }
 
 trait Dog{ 
 use Cat;
 public function drive(){ 
 echo "This is Dog drive";
 }
 abstract public function getName();
 
 public function test(){ 
 static $num=0;
 $num++;
 echo $num;
 }
 
 public static function say(){ 
 echo "This is Dog say";
 }
 }
 class animal{ 
 use Dog;
 public function getName(){ 
 echo "This is animal name";
 }
 }
 
 $animal = new animal();
 $animal->getName();
 echo " ";
 $animal->eat();
 echo " ";
 $animal->drive();
 echo " ";
 $animal::say();
 echo " ";
 $animal->test();
 echo " ";
 $animal->test();
 ?>

输出如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjA2NDAw_size_16_color_FFFFFF_t_70 2]

作者：奋斗live  
链接：https://www.jianshu.com/p/fc053b2d7fd1  
来源：简书  
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

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[489b5a2e1f714d54a62041101a433cc7.png]: /images/20220829/a872afcb7f3445499d5d351c7c5e964a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjA2NDAw_size_16_color_FFFFFF_t_70 1]: /images/20220829/cc2d2bb9857c4ee596616521016d45af.png
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