using System;

using System.Linq;

using System.Collections.Generic;

​

public record Person

{

    public int Age { get; set; }

    public string Name { get; set; }

    public override string ToString() => $"{Name} has {Age.ToString()} years!";

}

​

internal class PersonBuilder 

{

    private Person Person { get; init; }

    private PersonBuilder()

    {

        this.Person = new Person();

    }

    public static PersonBuilder Create()

    {

        return new PersonBuilder(); 

    }

    public PersonBuilder WithName(string name) 

    {

        this.Person.Name = name;

        return this;

    }

    public PersonBuilder WithAge(int age)

    {

        this.Person.Age = age;

        return this;

    }

    public Person Build()

    {

        return this.Person;

    }

}

​

// .NET 5 C#9

internal class PersonalBuilder

{

    private Person template = new Person();

    private Person working = new Person();

    public PersonalBuilder WithName(string name)

    {

        working = working with { Name = name };

        return this;

    }

    public PersonalBuilder WithAge(int age)

    {

        working = working with { Age = age };

        return this;

    }

    // not thread safe

    public Person Build()

    {

        var buildPerson = working with { };

        working = template with { };

        return buildPerson;

    }

}

​

public class Program

{

    public static void Main()

    {

        var rnd = new Random(123737);

        var names = new List<string> {"Andrei", "Vlad", "Adi"};

        var personalBuilder = new PersonalBuilder();

        var persons = Enumerable.Range(0, 10).Select(x => {     

            return new { 

                person1 = PersonBuilder

                    .Create()

                    .WithAge(rnd.Next(20, 30) + x)

                    .WithName(names[rnd.Next(0, 3)])

                    .Build(), 

                 person2 = personalBuilder

                     .WithName(names[rnd.Next(0, 3)])

                     .WithAge(rnd.Next(20, 30) + x)

                     .Build() 

                };

        });

        foreach (var pair in persons)

        {

            Console.WriteLine($"{pair.person1} vs {pair.person2}");

        }

    }

}