using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Text;

class Program
{
    static void Main()
    {
        var foo = new Foo();
        Console.WriteLine(foo);
        (foo.Something as IDictionary<string, string>).Add("6", "six");
        Console.WriteLine(foo);

    }
}

class Foo
{
    private readonly Dictionary<string, string> something;

    public Foo()
    {
        this.something = new Dictionary<string, string>();

        this.something.Add("1", "one");
        this.something.Add("2", "two");
        this.something.Add("3", "three");
        this.something.Add("4", "four");
        this.something.Add("5", "five");
    }

    public IReadOnlyDictionary<string, string> Something
    {
        get
        {
            return this.something;
            //return this.something.ToImmutableDictionary();
        }
    }

    public override string ToString()
    {
        var sb = new StringBuilder();
        foreach (var item in this.something)
        {
            sb.AppendLine($"{item.Key}: {item.Value}");
        }

        return sb.ToString();
    }
}