class-constants.php

<?php
class Foo {
    const BAR = "bat\n";
}

echo Foo::BAR;

// PHP 5.3+
$object = new Foo();
echo $object::BAR;

$string = 'Foo';
echo $string::BAR;

// PHP 7.0+
echo 'Foo'::BAR;

echo ('Foo')::BAR;

echo (function() { return 'Foo'; })()::BAR;

echo (Foo::CLASS)::BAR;

echo ['Foo'][0]::BAR;

function getFoo() {
    return 'Foo';
}

echo getFoo()::BAR;

class getFoo {
    static public function getStringStatic() {
        return 'Foo';
    }
    
    public function getString() {
        return 'Foo';
    }
}

echo getFoo::getStringStatic()::BAR;

$foo = new getFoo();
$foo->getString()::BAR;

$obj = new class() {
    public function getString() {
        return 'Foo';
    }
};

$obj->getString()::BAR;