How to Prevent PHP Class Constants From Being Overridden?

Starting with PHP 8.1, you can mark class constants as final (which would prevent them from being overridden in subclasses):

// PHP 8.1+
class A
{
    final public const FOO = 'foo';
}

Overriding final constants will result in an error:

// PHP 8.1+
class B extends A
{
    // Fatal error: B::FOO cannot override final constant A::FOO
    final public const FOO = 'bar';
}

This was not possible in versions of PHP prior to 8.1, as class constants could be overridden (as you can see in the example below):

class A
{
    public const FOO = 'foo';
}

class B extends A
{
    public const FOO = 'bar';
}

echo A::FOO; // 'foo'
echo B::FOO; // 'bar'

This behavior is still possible in PHP 8.1 if you don't mark class constants as final.