Amp\Coroutine::__construct PHP Method

    public function __construct(\Generator $generator)
    {
        $this->generator = $generator;
        /**
         * @param \Throwable|null $exception Exception to be thrown into the generator.
         * @param mixed $value Value to be sent into the generator.
         */
        $this->when = function ($exception, $value) {
            if ($this->depth > self::MAX_CONTINUATION_DEPTH) {
                // Defer continuation to avoid blowing up call stack.
                Loop::defer(function () use($exception, $value) {
                    ($this->when)($exception, $value);
                });
                return;
            }
            try {
                if ($exception) {
                    // Throw exception at current execution point.
                    $yielded = $this->generator->throw($exception);
                } else {
                    // Send the new value and execute to next yield statement.
                    $yielded = $this->generator->send($value);
                }
                if ($yielded instanceof Promise) {
                    ++$this->depth;
                    $yielded->when($this->when);
                    --$this->depth;
                    return;
                }
                if ($this->generator->valid()) {
                    $got = \is_object($yielded) ? \get_class($yielded) : \gettype($yielded);
                    throw new InvalidYieldError($this->generator, \sprintf("Unexpected yield (%s expected, got %s)", Promise::class, $got));
                }
                $this->resolve($this->generator->getReturn());
            } catch (\Throwable $exception) {
                $this->dispose($exception);
            }
        };
        try {
            $yielded = $this->generator->current();
            if ($yielded instanceof Promise) {
                ++$this->depth;
                $yielded->when($this->when);
                --$this->depth;
                return;
            }
            if ($this->generator->valid()) {
                $got = \is_object($yielded) ? \get_class($yielded) : \gettype($yielded);
                throw new InvalidYieldError($this->generator, \sprintf("Unexpected yield (%s expected, got %s)", Promise::class, $got));
            }
            $this->resolve($this->generator->getReturn());
        } catch (\Throwable $exception) {
            $this->dispose($exception);
        }
    }