Calling a Method Immediately After Object Creation in OOP in PHP

Let's say we have a class Arr that stores an array of numbers and can calculate the sum of these numbers using the method getSum. The numbers themselves are passed as an array to the object's constructor, and can also be added one by one using the method add:

<?php
	class Arr
	{
		private $numbers = [];
		
		public function __construct($numbers)
		{
			$this->numbers = $numbers;
		}
		
		public function add($number)
		{
			$this->numbers[] = $number;
		}
		
		public function getSum()
		{
			return array_sum($this->numbers);
		}
	}
?>

Here is an example of using the class Arr:

<?php
	$arr = new Arr([1, 2, 3]);
	
	$arr->add(4);
	$arr->add(5);
	
	echo $arr->getSum(); // will output 15
?>

It might be the case that we pass all the necessary numbers at the moment of object creation, and then immediately want to find their sum:

<?php
	$arr = new Arr([1, 2, 3]);
	echo $arr->getSum(); // will output 6
?>

If we don't plan to do any further manipulations with the object, then the code above can be rewritten more concisely: we can create an object and immediately call its method getSum:

<?php
	echo (new Arr([1, 2, 3]))->getSum(); // will output 6
?>

<?php
	class StringProcessor
	{
		private $str = '';
		
		public function __construct($text)
		{
			$this->str = $text;
		}
		
		public function append($text)
		{
			$this->str .= $text;
			return $this;
		}
		
		public function getValue()
		{
			return $this->str;
		}
		
		public function getLength()
		{
			return strlen($this->str);
		}
	}
?>

Suppose this class was used in the following way:

<?php
	$str = new Str('aaa');
	$str->append('bbb');
	$str->append('ccc');
	
	echo $str->getLength();
?>

Rewrite this code by calling the class on the spot.