instanceof Carbon失败了

Question

In my application I use something like the following

if($val instanceof Carbon)
...

unfortunately unless I previously use Carbon in the code (even if just Carbon::now();) it will always return false. Why?

Answer 1

You are using Laravel's class auto-loader. You've defined this at config/app.php:

'Carbon' => Carbon\Carbon::class,

... so when you run this for the first time:

Carbon::now();

... PHP needs a Carbon class that is not defined yet so class auto-loading gets triggered and Laravel loads the Carbon\Carbon namespace and defines a Carbon alias. Thus $val instanceof Carbon can return true if the variable has the correct type.

However, instanceof itself will not trigger class auto-loading. Documentation suggests it did that in the past but it no longer does:

Before PHP version 5.1.0, instanceof would call __autoload() if the class name did not exist.

Demo

(I admit I still don't have an explanation of how you can make $val be an instance of Carbon if you haven't loaded the class yet.)