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

代码:

<?php
//定义trait trait Dog{ public $name="dog"; public function bark(){ echo "This is dog"; } }//定义基类 class Animal{ public function eat(){ echo "This is animal eat"; } }//定义集成关系。 外加use trait定义的类,就可以实现多层集成了 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(); ?>

输出结果: 

This is cat drive
This is animal eat
This is dog 

各个类之间的关系


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
 
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();

?>

结果:

This is cat drive
This is dog eat

 更多用法

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

代码:

<?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();
?>

as 还可以修改方法的访问控制

代码:

<?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

代码:

<?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();
?>

 

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