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

This is cat drive
This is animal eat
This is dog 

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();

如下显示

This is cat drive
This is dog 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

This is trait1 eat
This is trait1 driveThis is trait1 eat
This is trait1 drive
This is trait2 eat
This is trait2 driv

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

This is animal name
This is Cat eat
This is Dog drive
This is Dog say
1
2

以上就是我对trait的总结，如有错误，还望指正

作者：依恋灬

链接：https://www.jianshu.com/p/fc053b2d7fd1

来源：简书

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