Why should you care?

ShopNest shipping cost (Standard, Express, StorePickup) should swap without editing checkout.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public interface IShippingStrategy { decimal Quote(decimal weightKg); }
public sealed class StandardShipping : IShippingStrategy
{
    public decimal Quote(decimal w) => 40 + w * 8;
}
public sealed class ExpressShipping : IShippingStrategy
{
    public decimal Quote(decimal w) => 80 + w * 15;
}
public sealed class Checkout
{
    private readonly IShippingStrategy _shipping;
    public Checkout(IShippingStrategy shipping) => _shipping = shipping;
    public decimal Total(decimal items, decimal weight) => items + _shipping.Quote(weight);
}

Console.WriteLine(new Checkout(new ExpressShipping()).Total(1000, 2));

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Checkout depends on IShippingStrategy.
• Inject Express or Standard.
• Same structure as many “calculator” DI registrations.

Practice next

1. Quote Standard vs Express.
2. Add StorePickup returning 0.
3. Select strategy from user choice.
4. Pass destination city into Quote.
5. Register strategies in a dictionary by code.

Remember

Interchangeable algorithms. Inject the strategy. Open for new options.

ShopNest shipping strategies

Buyer picks Express at checkout.

Outcome: Totals use ExpressShipping without if-else soup.