Innmind / Immutable

        foreach ($this->keys as $index => $key) {

            $newKey = $discriminator($key, $this->values->get($index));

            if ($map === null) {

                $type = gettype($newKey);

                $map = new self(

                    $type === 'object' ? get_class($newKey) : $type,

                    SequenceInterface::class

                );

            }

            $pair = $this->pairs->get($index);

        foreach ($this->values as $value) {

            $key = $discriminator($value);

            if ($map === null) {

                $type = gettype($key);

                $map = new Map(

                    $type === 'object' ? get_class($key) : $type,

                    SequenceInterface::class

                );

            }

            if ($map->contains($key)) {

                $map = $map->put(