C# Builder Design Pattern

The Builder Pattern is a creational design pattern that separates the construction of a complex object from its representation. Rather than relying on multiple constructors, it offers a fluent style approach, which enhances readability, flexibility, and error handling.

Key benefits include:

- Avoiding "telescoping constructors" (i.e., too many parameters)

- Ensuring object consistency through validation at each step

- Improving code maintainability, particularly for large projects

- Supporting immutable objects, making them thread-safe by default

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Let’s break down the code

Define the Object

public enum CarType
{
    Sedan,
    Crossover
};
public record Car
{
    public CarType Type;
    public int WheelSize;
}

Create the Builder

public class CarBuilder
{
    public static ISpecifyCarType Create()
    {
        return new Impl();
    }

    public interface ISpecifyCarType
    {
        public ISpecifyWheelSize OfType(CarType type);
    }

    public interface ISpecifyWheelSize
    {
        public IBuildCar WithWheels(int size);
    }

    public interface IBuildCar
    {
        public Car Build();
    }

    private class Impl :
      ISpecifyCarType,
      ISpecifyWheelSize,
      IBuildCar
    {
        private readonly Car car = new();

        public ISpecifyWheelSize OfType(CarType type)
        {
            car.Type = type;
            return this;
        }

        public IBuildCar WithWheels(int size)
        {
            switch (car.Type)
            {
                case CarType.Crossover when size < 17 || size > 20:
                case CarType.Sedan when size < 15 || size > 17:
                    throw new 
                    ArgumentException($"Wrong size of wheel for {car.Type}.");
            }
            car.WheelSize = size;
            return this;
        }

        public Car Build()
        {
            return car;
        }
    }
}

Using the Builder

  var car = CarBuilder.Create()
          .OfType(CarType.Crossover)
          .WithWheels(18)
          .Build();
  Console.WriteLine(car);