Consider using switch statements instead of multiple if ... else if on enumeration types

[bstordrup]

When performing different actions based on the value of an enumeration tipe (like the ZipEntrySource enumeration), I think it is worth considering switch statements or switch expression statements instead of repeated if else statements.

A test using BenchmarkDotNet gave these results:

// * Summary *

BenchmarkDotNet v0.15.0, Linux Linux Mint 22.1 (Xia)
Intel Core i7-4800MQ CPU 2.70GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET SDK 9.0.300
  [Host]     : .NET 9.0.5 (9.0.525.21509), X64 RyuJIT AVX2
  DefaultJob : .NET 9.0.5 (9.0.525.21509), X64 RyuJIT AVX2


| Method           | Mean       | Error   | StdDev  |
|----------------- |-----------:|--------:|--------:|
| IfElse           | 1,040.0 ns | 9.28 ns | 8.23 ns |
| Switch           |   326.4 ns | 6.23 ns | 6.12 ns |
| SwitchExpression |   291.7 ns | 5.76 ns | 7.08 ns |

The Benchmark class used was this:

public abstract class BenchmarkTestsBase<T>
{
    protected readonly int _iterations;
    protected readonly T[] _inputData;

    protected BenchmarkTestsBase(int iterations, Func<int, T> getInputItem)
    {
        _iterations = iterations;
        _inputData = new T[_iterations];

        for (int i = 0; i < _iterations; i++)
        {
            _inputData[i] = getInputItem(i);
        }
    }
}

public class SwitchVsIfElseOnEnumerationBenchmarkTests : BenchmarkTestsBase<ZipEntrySource>
{
    public SwitchVsIfElseOnEnumerationBenchmarkTests() :
        base(1000, idx => (ZipEntrySource)(idx % 6))
    { }

    [Benchmark]
    public void IfElse()
    {
        ZipEntrySource result;

        for (int i = 0; i < _iterations; i++)
        {
            if (_inputData[i] == ZipEntrySource.FileSystem)
            {
                result = ZipEntrySource.FileSystem;
            }
            else if (_inputData[i] == ZipEntrySource.Stream)
            {
                result = ZipEntrySource.Stream;
            }
            else if (_inputData[i] == ZipEntrySource.ZipFile)
            {
                result = ZipEntrySource.ZipFile;
            }
            else if (_inputData[i] == ZipEntrySource.WriteDelegate)
            {
                result = ZipEntrySource.WriteDelegate;
            }
            else if (_inputData[i] == ZipEntrySource.JitStream)
            {
                result = ZipEntrySource.JitStream;
            }
            else
            {
                result = ZipEntrySource.None;
            }
        }
    }

    [Benchmark]
    public void Switch()
    {
        ZipEntrySource result;

        for (int i = 0; i < _iterations; i++)
        {
            switch (_inputData[i])
            {
                case ZipEntrySource.FileSystem:
                    result = ZipEntrySource.FileSystem;
                    break;
                case ZipEntrySource.Stream:
                    result = ZipEntrySource.Stream;
                    break;
                case ZipEntrySource.ZipFile:
                    result = ZipEntrySource.ZipFile;
                    break;
                case ZipEntrySource.WriteDelegate:
                    result = ZipEntrySource.WriteDelegate;
                    break;
                case ZipEntrySource.JitStream:
                    result = ZipEntrySource.JitStream;
                    break;
                default:
                    result = ZipEntrySource.None;
                    break;
            }
        }
    }

    [Benchmark]
    public void SwitchExpression()
    {
        ZipEntrySource result;

        for (int i = 0; i < _iterations; i++)
        {
            result = _inputData[i] switch
            {
                ZipEntrySource.FileSystem => ZipEntrySource.FileSystem,
                ZipEntrySource.Stream => ZipEntrySource.Stream,
                ZipEntrySource.ZipFile => ZipEntrySource.ZipFile,
                ZipEntrySource.WriteDelegate => ZipEntrySource.WriteDelegate,
                ZipEntrySource.JitStream => ZipEntrySource.JitStream,
                _ => ZipEntrySource.None
            };
        }
    }
}

using a copy of the ZipEntrySource enumeration in the test.