gistfile1.cs

using System;
using Microsoft.Framework.DependencyInjection;

namespace weListen.Infrastructure.Workers.Sanitization
{
    public static class ExtensionMethods
    {
        public static IServiceCollection RegisterEngines(this IServiceCollection services)
        {
            return services.AddScoped<EngineA>()
                .AddScoped<EngineB>()
                .AddScoped<IEngine, EngineSelector>();
        }
    }

    public class EngineSelector : IEngine
    {
        private readonly EngineA _engineA;
        private readonly EngineB _engineB;

        public EngineSelector(EngineA engineA, EngineB engineB)
        {
            _engineA = engineA;
            _engineB = engineB;
        }

        public void DoStuff()
        {
            if (SelectA())
            {
                _engineA.DoStuff();
            }
            else
            {
                _engineB.DoStuff();
            }
        }

        private bool SelectA()
        {
            throw new NotImplementedException();
        }
    }

    public class EngineA : IEngine
    {
        public void DoStuff()
        {
        }
    }

    public class EngineB : IEngine
    {
        public void DoStuff()
        {
        }
    }

    public interface IEngine
    {
        void DoStuff();
    }
}