Finding the cheapest hotel

I thought this question made a good excuse for some basic OOP code, so I whipped up a little bit of code to demonstrate it in VBA; the idea is to have tutorial-grade code, to show how interfaces and default instances can be used to implement immutable types and factory methods to simulate constructors in VBA.

Here's the original problem statement:


A hotel chain operating in Goa wishes to offer room reservation services. They have three hotels in Goa: GreenValley, RedRiver and BlueHills. Each hotel has separate weekday and weekend (Saturday and Sunday) rates. There are special rates for rewards customer as a part of loyalty program. Each hotel has a rating assigned to it.

• GreenValley with a rating of 3 has weekday rates as Rs1100 for regular customer and Rs800 for rewards customer. The weekend rates are 900 for regular customer and 800 for a rewards customer.

• RedRiver with a rating of 4 has weekday rates as Rs1600 for regular customer and Rs1100 for rewards customer. The weekend rates are 600 for regular customer and 500 for a rewards customer.

• BlueHills with a rating of 5 has weekday rates as Rs2200 for regular customer and Rs1000 for rewards customer. The weekend rates are 1500 for regular customer and 400 for a rewards customer.

The input to the program will be a range of dates for a regular or rewards customer. The output should be the cheapest available hotel. In case of a tie, the hotel with highest rating should be returned.

I have this code in Module1:

```
Option Explicit

Public Sub Test(ByVal checkin As Date, ByVal checkout As Date, ByVal custType As CustomerType)
Dim finder As New HotelFinder
InitializeHotels finder
Debug.Print finder.FindCheapestHotel(checkin, checkout, custType)
End Sub

Private Sub InitializeHotels(ByVal finder As HotelFinder)

With StandardHotel.Create("Green Valley", 3)
.AddPricingRule FixedAmountPricingRule.Create(PricingRuleInfo.Create(WkDay, Premium), 800)
.A

I was not aware of the VB_PredeclaredId attribute and it's impact on VBA classes, so I've definitely learned something from your example. But I had to research it a bit in order to understand it. So, a few comments:

Your example is very good in terms of its ability to demonstrate the application of interfaces and default instances, especially in terms of VBA. What's less apparent here is the "teaching" aspects of your code -- this can easily be explained away here because this forum focuses only on code aspects and not (in your case) the supporting tutorial or explanations surrounding it. As an example, I think many (most?) VBA developers haven't run into the VB_PredeclaredId attribute and how to use it and even why it would be important in this context. (You have to understand the limitations of VBA classes and objects first, to know why it's applicable.)

My point is that while this is a very good example of reasonably standard OOP implementations in many languages, it seems specifically targeted at either a) experienced OOP devs proficient in other languages that have more direct language support for interfaces, implementations, and instancing; or b) advanced VBA devs that can learn how to implement factories using VBA. To use this code as a tutorial, you'll have to be mindful of the audience.

I started out in OOP with C++ and Ada (old skool!), so the concepts you're bringing out are very familiar. I like implementing a this type that mimics object accessors and using patterns like factories (particularly the hack to use with New syntax.

My comments are based on your opening line in the OP for "basic OOP code", which is largely true for other languages but I believe it's more of an advanced usage in VBA. Thanks for good things to learn!

StackExchange Code Review Q#133871, answer score: 3