PHP之Trait详解

新手劳工 發表於 2019-9-15 20:56:00

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<blockquote>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</blockquote>
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:
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<pre><?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();
?></pre>
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将会如下输出
 
<img class="origin_image zh-lightbox-thumb lazy" src="https://pic2.zhimg.com/80/v2-d90d5ed3bb0935c81126ed1719c5c81d_hd.jpg" alt="" width="474" data-caption="" data-size="normal" data-rawwidth="474" data-rawheight="234" data-original="https://pic2.zhimg.com/v2-d90d5ed3bb0935c81126ed1719c5c81d_r.jpg" data-actualsrc="https://pic2.zhimg.com/v2-d90d5ed3bb0935c81126ed1719c5c81d_b.jpg" data-lazy-status="ok">
<h3>再测试Trait、基类和本类对同名属性或方法的处理，如下代码</h3>
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<pre><?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();

?></pre>
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<img class="origin_image zh-lightbox-thumb lazy" src="https://pic1.zhimg.com/80/v2-f27fa4adbd84fe4a5840598784b5e388_hd.jpg" alt="" width="459" data-caption="" data-size="normal" data-rawwidth="459" data-rawheight="194" data-original="https://pic1.zhimg.com/v2-f27fa4adbd84fe4a5840598784b5e388_r.jpg" data-actualsrc="https://pic1.zhimg.com/v2-f27fa4adbd84fe4a5840598784b5e388_b.jpg" data-lazy-status="ok">
所以：Trait中的方法或属性会覆盖基类中的同名的方法或属性，而本类会覆盖Trait中同名的属性或方法
<h3>一个类可以组合多个Trait，通过逗号相隔，如下</h3>
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：
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<pre><?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();
?></pre>
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输出如下
 
<img class="origin_image zh-lightbox-thumb lazy" src="https://pic4.zhimg.com/80/v2-c710d1d33824e2cdaffe726d21e84233_hd.jpg" alt="" width="555" data-caption="" data-size="normal" data-rawwidth="555" data-rawheight="318" data-original="https://pic4.zhimg.com/v2-c710d1d33824e2cdaffe726d21e84233_r.jpg" data-actualsrc="https://pic4.zhimg.com/v2-c710d1d33824e2cdaffe726d21e84233_b.jpg" data-lazy-status="ok">
<h3>as 还可以修改方法的访问控制</h3>
<div class="cnblogs_code">
<pre><?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
?></pre>
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<h3>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</h3>
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<pre><?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();
?></pre>
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输出如下
 
<img class="origin_image zh-lightbox-thumb lazy" src="https://pic1.zhimg.com/80/v2-d93f6e8f6d4a0ba908d5c2c2734c76ac_hd.jpg" alt="" width="549" data-caption="" data-size="normal" data-rawwidth="549" data-rawheight="254" data-original="https://pic1.zhimg.com/v2-d93f6e8f6d4a0ba908d5c2c2734c76ac_r.jpg" data-actualsrc="https://pic1.zhimg.com/v2-d93f6e8f6d4a0ba908d5c2c2734c76ac_b.jpg" data-lazy-status="ok"></div>
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<div class="RichText ztext Post-RichText">最常见的应用场景就是将底层的curd用trait封装，然后在控制器中调用即可</div>
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<div class="RichText ztext Post-RichText">参考文章：https://zhuanlan.zhihu.com/p/81123521 </div>
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let the world have no hard-to-write code^-^ 
来源：https://www.cnblogs.com/ovim/p/11524193.html

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PHP之Trait详解