src/Lumper/Lumper.php
public function once(callable $callback, $unique = null)
    {
        $_ = (string)$this->_unique($callback, $unique);

        if (empty($this->instances[$_]))
        {
            $this->instances[$_] =
                $unique instanceof Slice ?
                    $callback($unique) :
                    $callback();
        }

        return $this->instances[$_];
    }
public function once(callable $callback, $unique = null)
    {
        $_ = (string)$this->_unique($callback, $unique);

        if (empty($this->instances[$_]))
        {
            $this->instances[$_] =
                $unique instanceof Slice ?
                    $callback($unique) :
                    $callback();
        }

        return $this->instances[$_];
    }
@param callable $callback
@param string   $unique

@return mixed