public List <FatValueType> StructLinq_IFunction()
        {
            var predicate = new FatValueTypeIsEven();
            var selector  = new DoubleOfFatValueType();

            return(source.ToRefStructEnumerable()
                   .Where(ref predicate, x => x)
                   .Select(ref selector, x => x, x => x)
                   .ToList(x => x));
        }
        public FatValueType StructLinq_IFunction()
        {
            var sum      = default(FatValueType);
            var selector = new DoubleOfFatValueType();

            foreach (var item in source
                     .ToRefStructEnumerable()
                     .Select(ref selector, x => x, x => x))
            {
                sum += item;
            }
            return(sum);
        }