php - Custom class method returns error

Question

    $input=new Input();
    $upSet=$input->post();
    var_dump($upSet);

class Input{
    function post($key){
        if(isset($_POST[$key])){
            $val=$_POST[$key];
            return $val;
        }
        
    }

报错
Warning: Missing argument 1 for Input::post(),
Notice: Undefined variable: key

Answer 1

Solution:

class Input{
  public function post($key){
        if(isset($_POST[$key])){
            $val=$_POST[$key];
            return $val;
        }
        
  }


$input=new Input();
$upSet=$input->post("demo");
var_dump($upSet);

Answer 2

function post($key = 'default'){}

Answer 3

Write less closing curly braces below the Input class }
In addition, there are no parameters passed in the post method