Are there pure virtual functions in PHP like with C++

问题

I would have thought lots of people would have wondered whether this is possible but I can't find any duplicate questions... do correct me.

I just want to know whether PHP offers pure virtual functions. I want the following

class Parent {
   // no implementation given
   public function foo() {
      // nothing 
   }
}

class Child extends Parent {
   public function foo() {
      // implementation of foo goes here
   }
}

Thanks very much.

回答1:

You can create abstract functions, but you need to declare the parent class as abstract, too:

abstract class Parent {
   // no implementation given
   abstract public function foo();
}

class Child extends Parent {
   public function foo() {
      // implementation of foo goes here
   }
}

回答2:

Declare the method as abstract in the Parent class:

abstract public function foo();

回答3:

There are abstract classes!

abstract class Parent {
   // no implementation given
   abstract public function foo();
   }
}

class Child extends Parent {
   public function foo() {
      // implementation of foo goes here
   }
}

回答4:

Yes, that type of solution is possible, it's called polymorphism, you can do it without declaring an abstract class or an interface.

来源：https://stackoverflow.com/questions/7600771/are-there-pure-virtual-functions-in-php-like-with-c