What is the difference between $this->$propertyName = $value and $this->propertyName = $value?

When setting private member attributes through __set($propertyName,$value),
use $this->$propertyName = $value to modify the private variable value,
use $ The writing rule of this->propertyName = $value cannot modify the variable value.

Full code:

class BasePerson{

<code>   private $name;
   private $age;
   private $average;
   function __construct(){
       $num_args = func_num_args();
       if($num_args == 1){
           $this->name = func_get_arg(0);
       } elseif($num_args == 2){
           $this->name = func_get_arg(0);
           $this->age = func_get_arg(1);
       } elseif($num_args == 3){
           $this->name = func_get_arg(0);
           $this->age = func_get_arg(1);
           $this->average = func_get_arg(2);
       }
   }
   
   private function __set($propertyName,$propertyValue){
       echo "</br>BasePerson __set()";
       if($propertyName == "name"){
           if($propertyValue == "zhangsan" || $propertyValue == "wangwu"){
               $this->$propertyName = $propertyValue;
           }
       } elseif($propertyName=="age"){
           if($propertyValue >150 || $propertyValue <0){
               return ;
           }
       }
       $this->$propertyName = $propertyValue;
   }
   
   function __toString(){
       return "</br>name:".($this->name)."</br>age:".($this->age)."</br>average".($this->average);
   }
</code>

}

Reply content:

When setting private member attributes through __set($propertyName,$value),
use $this->$propertyName = $value to modify the private variable value,
use $ The writing rule of this->propertyName = $value cannot modify the variable value.

Full code:

class BasePerson{

<code>   private $name;
   private $age;
   private $average;
   function __construct(){
       $num_args = func_num_args();
       if($num_args == 1){
           $this->name = func_get_arg(0);
       } elseif($num_args == 2){
           $this->name = func_get_arg(0);
           $this->age = func_get_arg(1);
       } elseif($num_args == 3){
           $this->name = func_get_arg(0);
           $this->age = func_get_arg(1);
           $this->average = func_get_arg(2);
       }
   }
   
   private function __set($propertyName,$propertyValue){
       echo "</br>BasePerson __set()";
       if($propertyName == "name"){
           if($propertyValue == "zhangsan" || $propertyValue == "wangwu"){
               $this->$propertyName = $propertyValue;
           }
       } elseif($propertyName=="age"){
           if($propertyValue >150 || $propertyValue <0){
               return ;
           }
       }
       $this->$propertyName = $propertyValue;
   }
   
   function __toString(){
       return "</br>name:".($this->name)."</br>age:".($this->age)."</br>average".($this->average);
   }
</code>

}

<code>$name = 'test';
$$name = '123';
var_dump($test);  //输出123
//希望你能理解

//同理
$this->$proertyName //需要看$proertyName的值, 是设置$proertyName的值这个属性
$proertyName = 'age';
$this->$proertyName = '12';
var_dump($this->age);  //输出12

$this->proertyName  //设置的是proertyName这个属性</code>

Original author, $this->$propertyName = $value Such an assignment is that the variable in the $this instance is the value of the $propertyName variable. The $propertyName here is still a variable, and $this->propertyName is the attribute of $this;

The former situation is like this, for example, $propertyName = 'enable';
then $this->$propertyName is equivalent to $this->enable;