With Rule::when() we can conditionally apply validation rules

Thanks to Rule::when() we can conditionally apply validation rules in laravel.

In this example we validate the value of the vote only if the user can actually vote the post.

use Illuminate\Validation\Rule;
 
public function rules()
{
    return [
        'vote' => Rule::when($user->can('vote', $post), 'required|int|between:1,5'),
    ]
}

Tip given by @cerbero90