private function compareReturnType()
{
$base = $this->base->getReturnType();
$challenger = $this->challenger->getReturnType();
if ($base !== $challenger) {
$message = 'return ' . $this->getTypeChangingMessage($base, $challenger);
$difference = new Difference($message);
$this->populateDifference($difference);
if (null !== $base && 'private' !== $this->base->getVisibility()) {
$difference->addTag(Difference::BC_BREAK);
}
$this->differences->add($difference);
}
}
