using System;

using System.Collections.Generic;

using Microsoft.Extensions.Configuration;

using Microsoft.Extensions.Configuration.Binder;

​

public class Program

{

    public static void Main()

    {

        var config = ConfigurationProvider.Instance;

        Console.WriteLine(config.GetValue<string>("test"));

    }

    class ConfigurationProvider 

    {

        private static IConfiguration _instance;

        public static IConfiguration Instance 

        {

            get 

            {

                if(_instance == null)

                {

                    _instance = new ConfigurationBuilder()

                        .AddInMemoryCollection(new Dictionary<string, string> 

                        {

                            { "test", "test1" }

                        })

                        .AddJsonFile($"appsettings.json", optional: true)

                        .AddEnvironmentVariables()

                        .Build();

                }

                return _instance;

            }

        }

    }

}