Why does "Constant expression contains invalid operations" error appear in connection class using PDO in PHP?

• Modify the position of the code to parse the INI file
• Add some attributes

• Add the use PDO, to avoid the global class error, avoid using \ in each PDO

  use PDO;
  class Conexion 
  {
      private $_host;
      private $_user;
      private $_pass;
      private $_dbname;
      private $_charset;
      private $_conexion; /* private $_conexion */
  
      public function __construct() {
          $archivo = 'config.ini.php';
          $configurar = parse_ini_file($archivo, true);
  
          $this->_host = $configurar['basedatos']['host'];
          $this->_user = $configurar['basedatos']['user'];
          $this->_pass = $configurar['basedatos']['pass'];
          $this->_dbname = $configurar['basedatos']['dbname'];
          $this->_charset = $configurar['basedatos']['charset'];
          try 
          {
  
          $this->_conexion = new PDO("mysql:host=$this->_host;
                  dbname=$this->_dbname;
                  charset=$this->_charset", 
                  $this->_user, 
                  $this->_pass);
           $this->_conexion->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                  echo "Conexion Exitosa"; 
          }
  
          catch(PDOException $e)
          {
              echo "Conexion Fallida: " . $e->getMessage();
          }
      }
  
      public function consultaSimple($sql) {
          $this->_conexion->query($sql);
      }
  
      public function consultaRetorno($sql) {
          $datos= $this->_conexion;
          return $datos;
      }
  }
  
  $conexion = new conexion();
  

Inside the PDO object, at the time of connection you can not use $ this-> Xvariable, I tell you from experience, it has happened to me, you must do it in the following way:

    private function __construct() {
        try 
        {
            self::$_conexion = new PDO("mysql:
                host=$host;
                dbname=$dbname;
                charset=$charset", 
                $this->_datos['user'], 
                $this->_datos['pass']);

            self::$_conexion->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                echo "Conexion Exitosa"; 
        }