public class Facility {
  private SharePie shares;
  . . .
  public SharePie calculateDrawdownDefaultDistribution(
                                  double drawdownAmount) {
    return shares.prorated(drawdownAmount);
  }
}

public class Loan {
  . . .
  public void applyDrawdown(SharePie drawdownShares) {
    setShares(shares.plus(drawdownShares));
  }
}
