Builder Pattern with Extension Method.cs

using System;

namespace Zjy.Utils
{
    public class Car {
        public string Make {get; set;}
        public string Model {get; set;}
        public string Year {get; set;}
        public int Mileage {get; set;}
        public decimal Price {get; set;}
        public void Save() {
            Console.WriteLine("Saved!");
        }
        public override string ToString() {
            return $"{Make} {Year} with mileage {Mileage} at Price: ${Price}";
        }
    }
    
    # region Builder Pattern
    public interface ICarBuilder
    {
        Car Car { get; }
        Car Build();
    }
    public class CarBuilder : ICarBuilder
    {
        private Car _car = null;
        public CarBuilder()
        {
            _car = new Car();
        }

        public Car Car => this._car;

        public Car Build()
        {
            this._car.Save();
            return this._car;
        }
    }
    # endregion
    
    # region Extension Methods
    /// <summary>
    /// We can add customized extensions to ICarBuilder.
    /// Even if we shipped following piece of code.
    /// </summary>
    public static class CarBuilderExtentions
    {
        public static ICarBuilder AddPrice(this ICarBuilder builder, decimal price)
        {
            builder.Car.Price = price;
            return builder;
        }

        public static ICarBuilder AddMileage(this ICarBuilder builder, int mileage)
        {
            builder.Car.Mileage = mileage;
            return builder;
        }
        public static ICarBuilder AddYear(this ICarBuilder builder, string year)
        {
            builder.Car.Year = year;
            return builder;
        }
        public static ICarBuilder AddMake(this ICarBuilder builder, string make)
        {
            builder.Car.Make = make;
            return builder;
        }
    }
    # endregion
    
    
    # region Usage
    public class Program {
        public static void Main(string[] args) {
            var car = new CarBuilder()
                            .AddMake("Honda")
                            .AddYear("2020")
                            .AddMileage(20000)
                            .AddPrice(10000m)
                            .Build();
            Console.WriteLine(car);
        }
    }
    # endregion
}

​Builder Pattern with Extension Method.output.txt

Saved!
Honda 2020 with mileage 20000 at Price: $10000

​​.sharplab.json

{
    "version": 1,
    "target": "Run",
    "mode": "Debug"
}