class demo{
    private $age;
    public function __construct($age){
            $this->age =$age;
    }
    public function __set($name,$value){
        if($name =='age'){
            return false;
        }       
        return $this->$name=$value;
    }   
}
    $obj =new demo(24);
    echo $obj->age=25;
    $obj->age=26;
    echo $obj->age;

In your code, the second echo should not be executed. You didn’t post the entire code, because it will prompt you that you cannot access private properties

The difference between the two output results is because of the way you write echo, echo a = 3 This way of writing will execute the assignment statement, but regardless of whether the assignment is successful, the number to the right of the equal sign will be output to the screen

1. The first echo $obj->age=25; executes your set method , it is obtained that name is equal to age, and return false is executed, so the value of the attribute age is not modified. But with your way of writing, it will output the 25 on the right side of your equal sign on the screen;

2. The second way is the normal way of writing, which will execute the assignment statement, then judge and return false, without modifying the value of age, and then Output the value of your age attribute is still 24

echo $obj->age=25 This statement is wrong. You did not change the value in the class. You just output a value of 25.

1. There should be something wrong in your set method. Look at your else statement, it seems like it’s missing

2. If you want to read private attributes, you need to write another get method

if($name =='age')
        {return false;}  //没有else     
return $this->$name=$value;
    }   
 }
     
   //正确代码
   public function __set($name,$value){
        if($name == 'age'){
            echo 'age不允许修改';
        }else{      
            return $this->$name = $value;
        } 
    } 
    
    public function __Get($name){
            return $this->$name;
    }