final public function pipe(callable $stage, callable $fallback = null): PipeChainInterface
    {
        $this->stack->attach($stage, $fallback);

        return $this;
    }
final public function pipe(callable $stage, callable $fallback = null): PipeChainInterface
    {
        $this->stack->attach($stage, $fallback);

        return $this;
    }
final public function pipe ( callable $ stage , callable $ fallback = null ) : PipeChainInterface { $ this -> stack -> attach ( $ stage , $ fallback ) ; return $ this ; }
pipes a stage with an optional associated fallback.

@param callable $stage
@param callable $fallback
@return PipeChainInterface
pipes a stage with an optional associated fallback .