Blog_LinqVsBoringOld.cs

[MemoryDiagnoser]
public class LinqPitfall
{
    private static readonly int[] source = Enumerable.Range(1, 100_000).ToArray();

    private readonly HashSet<int> forbidden = new HashSet<int>
    {
        123, 234, 345, 456, 567, 678, 789, 890, 901, 1000
    };

    [Benchmark]
    public int[] Linq()
    {
        return source
            .Where(x => !forbidden.Contains(x))
            .Select(x => x * 2)
            .ToArray();
    }

    [Benchmark(Baseline = true)]
    public int[] BoringOld()
    {
        // we can predict a lot of data is in compliance
        var result = new List<int>(source.Length);

        foreach (var x in source)
        {
	    if (!forbidden.Contains(x))
	    {
	        result.Add(x * 2);
            }
        }
        return result.ToArray();
    }
}