括号是什么意思？

Question

class Util_Model
{
/**
 * Get model property by property name chain.
 * Usage: Util_Model::get_prop($order, 'item', 'name')
 */
public static function get_prop()
{
    $obj  = func_get_arg(0);
    $props = array_slice(func_get_args(), 1);

    if (!is_object($obj)) {
        throw new \InvalidArgumentException('First parameter must be an object');
    }

    foreach ($props as $prop) {
        if (preg_match('/^(.*)\(\)$/', $prop, $matches)) {
            $obj = call_user_func(array($obj, $matches[1]));
        } else {
            $obj = $obj->{$prop};
        }
        if (!is_object($obj)) {
            break;
        }
    }

    return is_object($obj) ? (string)$obj : $obj;
}
}

$obj->{$prop} i wonder the meaning of this line, why there is a brace here? and why there is no error when {$prop} is null.if you don't understand my question, leave something I will amend it.thanks!

Answer 1

$obj->{$prop} means that $obj is trying to access a property whose name is present in the variable $prop. I'll explain with an example

class A {
     public $d;
     public $e;
     public $f;
     function X() {}
     function Y() {}
     function Z() {}
}

$obj = new A();
$prop = 'X';
$propVar = 'f';
$obj->{$prop}();
$obj->{$propVar};

In the above code, $prop contains the value 'X', so function X will be invoked, likewise if it was containing values 'Y' or 'Z', they would be invoked. So the invocation of function can be decided at runtime depending on the value the variable contains.

As for the case when $prop is null, no object is being accessed, so the reference of object is returned instead and no error is thrown.