# Reference solution — end state of exercise 3

Derived from [IceCreamForecasting-Refactoring-Kata](https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata)
(same license as the kata applies to the copied `IceCream.cs`).

Run with `dotnet test test/BuyersTests.csproj` — the test passes deterministically
without touching the pricing service.

## What changed vs the exercise start

1. The pricing call extracted into a lambda and slid to the top:
   `Func<IceCream, int> priceFor = flavour => priceList.PriceFor(flavour);`
   — the invocation in the loop stays put (`priceFor(flavour)`).
2. The loop extracted to
   `ShoppingListTotal(Buyer buyer, Func<IceCream, int> priceFor)` — static-free of
   `PriceList`; all inputs are parameters. (C# note: this one is an instance method
   because `ByName` uses the `buyers` field; the *extracted loop method itself*
   touches no fields. If you want it `static`, extract the loop only and keep the
   lookup in the composed method.)
3. No-arg `ShoppingListTotal(string)` overload keeps callers working; it passes the
   method group `priceList.PriceFor` as the "real" pricing function.
4. The test passes a pure lambda (`_ => 2`) through the overload — deterministic,
   glanceable: 2 flavours × 2 scoops × 2 = 8.

## Intermediate step (between pristine and this solution)

```csharp
public int ShoppingListTotal(string buyerName)
{
    Func<IceCream, int> priceFor = flavour => priceList.PriceFor(flavour); // ← extracted & slid
    var buyer = ByName(buyerName);
    var total = 0;
    foreach (var flavour in buyer.Favourites)
    {
        total += buyer.ScoopsOf(flavour) * priceFor(flavour);              // ← invocation stays
    }
    return total;
}
```

## Variations (debrief / second round)

- `_ => 5` — everything costs 5: Anke 20, Bram 10, Celine 20.
- `flavour => flavour == IceCream.Chocolate ? 10 : 1` — chocolate is expensive.
- Delete `PriceList` entirely: the extracted method no longer knows it exists —
  a step-4 move is now unblocked (move `ShoppingListTotal(Buyer, Func)` to a
  class without `PriceList`).
- Role-interface next step: add `DiscountFor(IceCream)` to `PriceList` (a second
  side-effectful method) and feel why one lambda is no longer enough — extract
  `IPricing` instead.