Typically trying to extend the parent like so:
.parent {
style: value;
@extend &;
}
Will result in an error, stating that the parent cannot be extended. This makes sense, but there's a workaround. Simply store the parent selector in a variable.
.parent {
$parent: &;
style: value;
@extend #{&};
}
There's no benefit to doing this in the above example, however this gives you the power to wrap parent styles from within an included mixin.