C#

using System;
using System.Runtime.InteropServices;

namespace Simple
{
    class DLLPlugin
    {        
        [DllImport("kernel32", EntryPoint = "LoadLibrary")]
        private static extern IntPtr LoadLibrary(string lpLibFileName);
        [DllImport("kernel32", EntryPoint = "GetProcAddress", SetLastError = true)]
        private static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);
        [DllImport("kernel32", EntryPoint = "FreeLibrary", SetLastError = true)]
        private static extern bool FreeLibrary(IntPtr hModule);

        public delegate void VoidVoidDelegate();
        
        private VoidVoidDelegate RunDelegate;
        private IntPtr moduleRef;

        public DLLPlugin(string dllName)
        {
            moduleRef = LoadLibrary(dllName);
            IntPtr pfn = GetProcAddress(moduleRef, "Run");
            RunDelegate = (VoidVoidDelegate)
                Marshal.GetDelegateForFunctionPointer(pfn, typeof(VoidVoidDelegate));
        }

        ~DLLPlugin()
        {
            FreeLibrary(moduleRef);
        }

        public void Run()
        {
            RunDelegate();
        }
    }
}

public delegate void VoidVoidDelegate();
private VoidVoidDelegate RunDelegate;