在 PHP 中链接方法并将第一个调用的方法作为最后一个执行，它是如何工作的？

Question

I'm working with Laravel for a little while now and since the start I have been wondering how they are able to chain methods in a random order and still execute the whole chain as one operation.

For example, in the console kernel:

protected function schedule(Schedule $schedule)
{
    $schedule->command('some-command')
        ->everyThirtyMinutes()
        ->before(function (Schedule $schedule) {
            $schedule->command('some-other-command');
        });
}

The command method is called first, but the command will only run every thirty minutes. That information came after calling the command method, but is still processed before executing it. The same goes for the before method. That method is called last, but the some-other-command command is still being executed first.

I've searched the internet for the answer, but I couldn't find one. I hope you know the answer.

Answer 1

That method is called last, but the some-other-command command is still being executed first.

Because that is what the before() method does, placing another command before (hence the name) the current command. And as the class name Scheduler implies, it's setting up some schedule, not executing the code as is, so the question is rather a misunderstanding of what the code does.

Answer 2

It depends on the context where you are using the chaining, in your example the first method is command :

Add a new Artisan command event to the schedule.

And it returns an Event , this Event instance has a lot of methods that you can call in chaining mode because they return $this witch mean they return the current instance of the event, so that you can call an other method that the Event` class offers.

In your example

• everyThirtyMinutes

Schedule the event to run every thirty minutes.
Return Value: $this

• before

Register a callback to be called before the operation .
Return Value: $this

Concerning the order you have to call command first to get the Event instance, and for the tow other methods the order has no effect.

Like if you told to someone go to the market every thirty minutes and before each time close the house door, it's the same thing if you told him (or her) before you go to the market close the house door and go every thirty minutes.