System.Data.UnaryNode.EvalUnaryOp C# (CSharp) Метод

        private object EvalUnaryOp(int op, object vl)
        {
            object value = DBNull.Value;

            if (DataExpression.IsUnknown(vl))
                return DBNull.Value;

            StorageType storageType;
            switch (op)
            {
                case Operators.Noop:
                    return vl;
                case Operators.UnaryPlus:
                    storageType = DataStorage.GetStorageType(vl.GetType());
                    if (ExpressionNode.IsNumericSql(storageType))
                    {
                        return vl;
                    }
                    throw ExprException.TypeMismatch(ToString());

                case Operators.Negative:
                    // the have to be better way for doing this..
                    storageType = DataStorage.GetStorageType(vl.GetType());
                    if (ExpressionNode.IsNumericSql(storageType))
                    {
                        switch (storageType)
                        {
                            case StorageType.Byte:
                                value = -(byte)vl;
                                break;
                            case StorageType.Int16:
                                value = -(short)vl;
                                break;
                            case StorageType.Int32:
                                value = -(int)vl;
                                break;
                            case StorageType.Int64:
                                value = -(long)vl;
                                break;
                            case StorageType.Single:
                                value = -(float)vl;
                                break;
                            case StorageType.Double:
                                value = -(double)vl;
                                break;
                            case StorageType.Decimal:
                                value = -(decimal)vl;
                                break;
                            case StorageType.SqlDecimal:
                                value = -(SqlDecimal)vl;
                                break;
                            case StorageType.SqlDouble:
                                value = -(SqlDouble)vl;
                                break;
                            case StorageType.SqlSingle:
                                value = -(SqlSingle)vl;
                                break;
                            case StorageType.SqlMoney:
                                value = -(SqlMoney)vl;
                                break;
                            case StorageType.SqlInt64:
                                value = -(SqlInt64)vl;
                                break;
                            case StorageType.SqlInt32:
                                value = -(SqlInt32)vl;
                                break;
                            case StorageType.SqlInt16:
                                value = -(SqlInt16)vl;
                                break;
                            default:
                                Debug.Assert(false, "Missing a type conversion");
                                value = DBNull.Value;
                                break;
                        }
                        return value;
                    }

                    throw ExprException.TypeMismatch(ToString());

                case Operators.Not:
                    if (vl is SqlBoolean)
                    {
                        if (((SqlBoolean)vl).IsFalse)
                        {
                            return SqlBoolean.True;
                        }
                        else if (((SqlBoolean)vl).IsTrue)
                        {
                            return SqlBoolean.False;
                        }
                        throw ExprException.UnsupportedOperator(op);  // or should the result of not SQLNull  be SqlNull ?
                    }
                    else
                    {
                        if (DataExpression.ToBoolean(vl) != false)
                            return false;
                        return true;
                    }

                default:
                    throw ExprException.UnsupportedOperator(op);
            }
        }