Instructions for using Trait in php

* What is Trait?

* 1. Trait is a code reuse mechanism tailored for single inheritance languages;

* 2. Previously, code could be implemented through functions or classes Reuse;

* 3. Trait can be simply understood as a collection of class methods, working between the parent class and subclass;

* 4. But trait is not limited to methods Collections also support abstraction, static and attributes;

* 5. The current class members will overwrite the trait class members, and the members in the trait can override the class members with the same name

* 6. Important Tip: Trait is not a class and cannot be instantiated. Remember

//Declare the parent class: Person

if (!class_exists('Person')) {
  class Person
    {
        protected $name;
        
        public function __construct($name='小明')
        {
            $this->name = $name;
        }
        
        public function study($course='php')
        {
            return $this->name.'在学习'.$course;
        }
    
        
    }  
}

//Declare the trait class: Course Course

if(!trait_exists('Course')){
    trait Course
    {
        //trait中也可以自己的属性
        public $friend='小华';
        public function sport($name='踢足球')
        {
//            return $this->name.'在学习'.$name;
            //trait中可以访问父类中的属性
            return $this->name.'和'.$this->friend.'在学习'.$name;
        } 
        
        //trait中同样支持抽象,以及静态方法,我放在一起写了
        //我把这个方法声明为抽象的同时,也声明为静态
        abstract public static function hobby($name);
        
        
        //在trait中也声明一个与父类同名的study()方法,参数修改一下以示区别
        public function study($course='java')
        {
            return $this->name.'在学习'.$course;
        }
    }
}

//Declare trait class: Recreation Entertainment

if(!trait_exists('Recreation')){
    trait Recreation
    {
        //这个trait类中也声明一个与Course中同名的方法sport
        //注意: 属性$friend不允许与Course::sport()同名
        //因为目前trait中还没有处理同名属性的机制,期待新版本会解决
        //这里我们将$friend 修改为 $friend1
        public $friend1='小军';
        public function sport($name='打蓝球')
        {
//            return $this->name.'在学习'.$name;
            //trait中可以访问父类中的属性
            return $this->name.'和'.$this->friend1.'在学习'.$name;
        } 
        
        
    }
}

Declare subclass: Student, inherited from parent class: Person

class Student extends Person
{
    //导入trait类
//    use Course;
    
    //子类支持导入多个trait类,但不可避免的会遇到方法重名问题,怎么解决呢?
//    use Course, Recreation;  //同时引入二个trait类
    //如果这二个trait类中有重名方法,要用以下语句结构解决
    use Course, Recreation {
        //访问sport()方法冲突时,使用Course::sport()代替掉Recoreation::sport()
        Course::sport insteadof Recreation;
       
        //再访问Recoreation::sport()时启用别名 mySport()
        Recreation::sport as mySport;
    }
    
    //子类中必须实现trait中声明的抽象方法hobby()
    public static function hobby($name)
    {
        return $name;
    }
    
    //在子类中再声明一个与trait类同名的study()方法,参数修改一下以示区别
    public function study($course='python')
    {
        return $this->name.'在学习'.$course;
    }
    
}

/ /Instantiate the Student class

$student = new Student();

//1. Access the methods in the parent class Person

echo $student->study();
echo &#39;<hr>&#39;;

//2. Access the methods in the trait class

echo $student->sport();
echo &#39;<hr>&#39;;

//3 To call abstract static methods in a trait, you must use Student to access them

echo Student::hobby('抽烟喝酒烫头');
echo &#39;<hr>&#39;;

//4. When a trait has a method with the same name as the parent class, the trait priority is higher

echo $student->study();

// 5. When there is a method with the same name as the trait class in a subclass, the subclass has a higher priority

echo $student->study();
echo &#39;<hr>&#39;;

//6. The subclass can obtain method sets from multiple traits

echo $student->sport();
echo &#39;<hr>&#39;;
echo $student->mySport();

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