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CSharp · Console

/Program.cs

using System;
using System.Reflection;

namespace Oooo
{
    class Base
    {
        public int Some { get; private set; }

        public Base()
        {
            Some = 12345;
        }
    }

    class Der : Base { }

    public class Program
    {
        public static void Main()
        {
            Der d = new Der();
            d.GetType()
                .GetProperty("Some")
                .DeclaringType
                .GetProperty("Some", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                .SetValue(d, 12, BindingFlags.NonPublic | BindingFlags.Instance, null, null, null);
            Console.WriteLine(d.Some);
        }

    }
}