Create a Last-In, First-Out (LIFO) Stack with PHP Arrays

<?php
class SimpleStack
{
    private array $stack = [];

    public function push(mixed $item): void
    {
        array_push($this->stack, $item);
        echo "Pushed: " . (is_array($item) ? json_encode($item) : $item) . "
";
    }

    public function pop(): mixed
    {
        if ($this->isEmpty()) {
            echo "Stack is empty, cannot pop.
";
            return null;
        }
        $item = array_pop($this->stack);
        echo "Popped: " . (is_array($item) ? json_encode($item) : $item) . "
";
        return $item;
    }

    public function peek(): mixed
    {
        if ($this->isEmpty()) {
            echo "Stack is empty, no item to peek.
";
            return null;
        }
        $item = end($this->stack); // Get the last element without removing it
        reset($this->stack); // Reset internal pointer
        echo "Peeked: " . (is_array($item) ? json_encode($item) : $item) . "
";
        return $item;
    }

    public function isEmpty(): bool
    {
        return empty($this->stack);
    }

    public function size(): int
    {
        return count($this->stack);
    }

    public function __toString(): string
    {
        return "Stack content: [" . implode(", ", array_map(function($item) {
            return is_array($item) ? json_encode($item) : (string)$item;
        }, $this->stack)) . "]
";
    }
}

$stack = new SimpleStack();
$stack->push(10);
$stack->push('hello');
$stack->push(['user_id' => 123]);
echo $stack;

$stack->pop();
echo $stack;

$stack->peek();
echo $stack;

$stack->pop();
$stack->pop();
$stack->pop(); // Attempt to pop from an empty stack
echo $stack;
?>