Question

class A{
  const FOO = 1;
}

class B extends A{

  const FOO = 5;

  function foo(){
    print self::FOO;
    print static::FOO;
  }
}

$b = new B;
$b->foo();

It prints 5 in both cases.

So there’s no difference in using static vs self on constants?

Answer 1

In the context of Late Static Binding there is a difference.

Consider this code:

<?php

class A {
    const FOO = 1;

    function bar() {
        print self::FOO;
        print "\n";
        print static::FOO;
    }
}

class B extends A {
    const FOO = 5;
}

$b = new B;
$b->bar();  // 1 5

If you run this code, the output will be:

1
5

When referencing self::FOO, the value of 1 is printed (even though bar() was called on class B, but when the static keyword was used, late static binding took effect and it referenced the FOO constant from B rather than A when using the static keyword.

This is relevant for PHP 5.3 and later.