How to implement and extend Joshua's builder pattern in .net?

Question

• How can we implement the Builder pattern of Joshua\'s Effective Java in C#?

Below is the code I have tried, is there a better way to do this?

Answer 1

The reason to use Joshua Bloch's builder pattern was to create a complex object out of parts, and also to make it immutable.

In this particular case, using optional, named parameters in C# 4.0 is cleaner. You give up some flexibility in design (don't rename the parameters), but you get better maintainable code, easier.

If the NutritionFacts code is:

  public class NutritionFacts
  {
    public int servingSize { get; private set; }
    public int servings { get; private set; }
    public int calories { get; private set; }
    public int fat { get; private set; }
    public int carbohydrate { get; private set; }
    public int sodium { get; private set; }

    public NutritionFacts(int servingSize, int servings, int calories = 0, int fat = 0, int carbohydrate = 0, int sodium = 0)
    {
      this.servingSize = servingSize;
      this.servings = servings;
      this.calories = calories;
      this.fat = fat;
      this.carbohydrate = carbohydrate;
      this.sodium = sodium;
    }
  }

Then a client would use it as

 NutritionFacts nf2 = new NutritionFacts(240, 2, calories: 100, fat: 40);

If the construction is more complex this would need to be tweaked; if the "building" of calories is more than putting in an integer, it's conceivable that other helper objects would be needed.