ConfigResolver.php
public function addCallback(VariationInterface $variation)
    {
        $closure = (function () {
            if (!$this->isValid()) {
                $this->doRewind();
            }

            return $this->getCurrent();
        })->bindTo($variation, $variation);
        $this->contextCallbacks[$variation->getName()] = $closure;

        return true;
    }
public function addCallback(VariationInterface $variation)
    {
        $closure = (function () {
            if (!$this->isValid()) {
                $this->doRewind();
            }

            return $this->getCurrent();
        })->bindTo($variation, $variation);
        $this->contextCallbacks[$variation->getName()] = $closure;

        return true;
    }
@param VariationInterface $variation

@return bool