Program.cs

    [MemoryDiagnoser]
    public class BenchmarkDemo2
    {
        private static readonly string _dateString = "01 05 1991";
        
        [Benchmark(Baseline = true)]
        public DateTime Original()
        {
            var day = _dateString.Substring(0, 2);
            var month = _dateString.Substring(3, 2);
            var year = _dateString.Substring(6);
            return new DateTime(int.Parse(year), 
                                int.Parse(month), 
                                int.Parse(day));
        }

        [Benchmark]
        public DateTime Span()
        {
            ReadOnlySpan<char> dateSpan = _dateString;
            var day = dateSpan.Slice(0, 2);
            var month = dateSpan.Slice(3, 2);
            var year = dateSpan.Slice(6);
            return new DateTime(int.Parse(year), 
                                int.Parse(month), 
                                int.Parse(day));
        }
    }