Confirm

class WebService {
	void setPassword(ValidPassword password, Confirm!"password" password_confirmation)
	{
		// password is valid and guaranteed to equal password_confirmation
	}

	void setProfileInfo(string full_name, Nullable!ValidPassword password, Nullable!(Confirm!"password") password_confirmation)
	{
		// Password is valid and guaranteed to equal password_confirmation
		// It is allowed for both, password and password_confirmation
		// to be absent at the same time, but not for only one of them.
	}
}