如何从父抽象类访问类属性到静态方法？

Here is a simple example.

abstract class A{
  protected $foo = 'I m foo'; 
}

class B extends A{
  static function sayFoo(){
     // get the value of $foo here. 
  }
}

I can pass foo as a constant, or change the function from static to normal, or declare sayFoo inside the parent class but I want to check if there is another way first without using Reflection

You can't access the protected $foo property statically because it isn't declared static. However you could if it was an object. One way to go about this is instantiate the class inside of your static function.

<?php

abstract class A{
  protected $foo = 'I m foo'; 
}

class B extends A{
  static function sayFoo(){
     // get the value of $foo here. 
      $bar = new self();
      echo $bar->foo;
  }
}   

B::sayFoo(); //prints 'I m foo';

?>