References in a class to static class members (fields or methods) can be made using either self::$var or static::$var
(introduced in 5.3). The difference between the two is one of scope. Confusingly, in subclasses, the use of self:: references the
original definition of the member, i.e. the superclass version, rather than any override at the subclass level. static::, on the other
hand, references the class that was called at runtime.
Noncompliant code example
<?php
class Toy {
public static function status() {
self::getStatus(); // Noncompliant; will always print "Sticks are fun!" even when called from a subclass which overrides this method;
}
protected static function getStatus() {
echo "Sticks are fun!";
}
}
class Ball extends Toy {
protected static function getStatus() { // Doesn't actually get called
echo "Balls are fun!";
}
}
$myBall = new Ball();
$myBall::status(); // Prints "Sticks are fun!"
Compliant solution
<?php
class Toy {
public static function status() {
static::getStatus(); // Compliant
}
protected static function getStatus() {
echo "Sticks are fun!";
}
}
class Ball extends Toy {
protected static function getStatus() {
echo "Balls are fun!";
}
}
$myBall = new Ball();
$myBall::status(); // Prints "Balls are fun!"
Exceptions
No issue is raised when self is used on a constant field, a private field or a private method.
class A
{
private static $somevar = "hello";
const CONSTANT = 42;
private static function foo()
{
$var = self::$somevar . self::CONSTANT; // Should be OK
self::foo(); // Should be OK
}
}
