PHP之Trait详解

Posted 2022-11-02 yulongcode

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 "<br/>";
$cat->eat();
echo "<br/>";
$cat->bark();
?>

 

将会如下输出

 

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 "<br/>";
$cat->eat();

?>

 

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

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 "<br/>";
$cat->drive();
echo "<br/>";
echo "<br/>";
echo "<br/>";
$dog = new dog();
$dog->eat();
echo "<br/>";
$dog->drive();
echo "<br/>";
$dog->eaten();
echo "<br/>";
$dog->driven();
?>

 

输出如下

 

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 "<br/>";
$animal->eat();
echo "<br/>";
$animal->drive();
echo "<br/>";
$animal::say();
echo "<br/>";
$animal->test();
echo "<br/>";
$animal->test();
?>

 

输出如下

 

 

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

 

参考文章：https://zhuanlan.zhihu.com/p/81123521