Stack.php

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<?php

declare(strict_types=1);

namespace ILIAS\components\DataCollection\Fields\Formula\FormulaParser;

class Stack
{
    protected array $stack = [];

    public function push($elem): void
    {
        $this->stack[] = $elem;
    }

    public function pop()
    {
        if (!$this->isEmpty()) {
            $last_index = count($this->stack) - 1;
            $elem = $this->stack[$last_index];
            unset($this->stack[$last_index]);
            $this->stack = array_values($this->stack); // re-index

            return $elem;
        }

        return null;
    }

    public function top()
    {
        if (!$this->isEmpty()) {
            return $this->stack[count($this->stack) - 1];
        }

        return null;
    }

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

    public function reset(): void
    {
        $this->stack = [];
    }

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