没有任何方法使用界面有什么好处？ 在PHP中

Question

AS I was looking at code in Laravel 5 project, I encountered with a class Like below --

class Abc extends Command implements SelfHandling, ShouldBeQueued
{

}

And where Interfaces are like below -

interface SelfHandling {}
interface ShouldBeQueued {}

I got confused if it does not have any methods then what's the use of these interfaces ?

Answer 1

It allows to handle objects by behavior. Say you have an array of objects implementing different interface, you can then differentiate them doing this :

if($obj instanceof ShouldBeQueued){
    //do something
}
else if{$obj instanceof SelfHandling){
    //do something else
}

This example is a bit crude, but I hope it will help you.

Answer 2

They are used as sort of a "flag". It can be checked by doing $command instanceof ShouldBeQueued .

The alternative would be to include a method, but that would require multiple lines of redundant code. (Most implementations would return true anyway.)

interface ShouldBeQueued
{
    /**
     * @return bool
     */
    function shouldBeQueued();
}

class Abc extends Command implements ShouldBeQueued
{
    function shouldBeQueued()
    {
        return true;
    }
}

Checking it would be a bit more complicated as well:

if ($command instanceof ShouldBeQueued && $command->shouldBeQueued()) { /*...*/ }

Whether it is a good practice is another matter.