In C#: How to declare a generic Dictionary with a type as key and an IEnumerable of that type as value?

Use System.ComponentModel.Design.ServiceContainer that is already available in .Net framework.

        ServiceContainer container = new ServiceContainer();

        IList<int> integers = new List<int>();
        IList<string> strings = new List<string>();
        IList<double> doubles = new List<double>();

        container.AddService(typeof(IEnumerable<int>), integers);
        container.AddService(typeof(IEnumerable<string>), strings);
        container.AddService(typeof(IEnumerable<double>), doubles);