Builder design pattern: Why do we need a Director?

Question

Recently I\'ve come across the Builder design pattern. It seems that different authors use \"Builder pattern\" to refer to different flavours, so let me describe the pattern

Answer 1

If you separate into Director and Builder you have documented the different responsibility of assembling a product from a set of parts (director) and the responsibility of creating the part (builder).

• In the builder you can change how a part is build. In your case whether a AddLiquid() should add cream or milk.
• In the director you can change how to assemble the parts. In your case a by using AddChocolate() instead of AddFruits() you get a different cake.

If you want this extra flexibility, I would rename to (since using baker in the builder suggests, it was the builders job of assembling the parts)

class LightBakingSteps : public BakingSteps {
public:
    virtual void AddLiquids()
    {
        // Add milk instead of cream
    }

    virtual void AddDryIngredients()
    {
        // Add light sugar
    }

    ...
};

class ChoclateCakeBaker : public CakeBaker {
public:
     Cake Bake(BakingSteps& steps)
     {
         steps.AddLiquieds();
         steps.AddChocolate();      // chocolate instead of fruits
         return builder.getCake();
     }
}