PHP之Trait詳解

php從之前到如今一直都是單繼承的語言，沒法同時從兩個基類中繼承屬性和方法，爲了解決這個問題，php出了Trait這個特性

 

用法：經過在類中使用use 關鍵字，聲明要組合的Trait名稱，具體的Trait的聲明使用Trait關鍵詞，Trait不能實例化

以下代碼實例:

<?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();
?>

 

將會以下輸出

This is cat drive
This is animal eat
This is dog 

 

再測試Trait、基類和本類對同名屬性或方法的處理，以下代碼

 
<?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();

 

以下顯示

This is cat drive
This is dog eat

 

因此：Trait中的方法或屬性會覆蓋 基類中的同名的方法或屬性，而本類會覆蓋Trait中同名的屬性或方法

一個類能夠組合多個Trait，經過逗號相隔，以下

use trait1,trait2

當不一樣的trait中，卻有着同名的方法或屬性，會產生衝突，能夠使用insteadof或 as進行解決，insteadof 是進行替代，而as是給它取別名

以下實例：

<?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();
?>

輸出以下

This is trait1 eat
This is trait1 drive




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

as 還能夠修改方法的訪問控制

<?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();//報錯，由於已經把eat改爲了保護


$cat = new Cat();
$cat->eat();//正常運行，不會修改原先的訪問控制
$cat->eaten();//報錯，已經改爲了私有的訪問控制
?

Trait也能夠互相組合，還能夠使用抽象方法，靜態屬性，靜態方法等，實例以下

<?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();
?

輸出以下

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

以上就是我對trait的總結，若有錯誤，還望指正

 

做者：依戀灬

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

來源：簡書

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