public int StructLinq_IFunction()
        {
            var sum      = 0;
            var comparer = new DefaultStructEqualityComparer();

            foreach (var item in source.ToStructEnumerable().Distinct(comparer, x => x))
            {
                sum += item;
            }
            return(sum);
        }
    public int StructLinq_ValueDelegate()
    {
        var comparer = new DefaultStructEqualityComparer();
        var distinct = source.ToStructEnumerable()
                       .Distinct(comparer, x => x);
        var sum = 0;

        foreach (var item in distinct)
        {
            sum += item;
        }
        return(sum);
    }