ReadOnly vs Immutable vs Frozen collection benchmarks

benchmark-results.csv

benchmark-results.md

BenchmarkDotNet v0.13.11, Windows 11 (10.0.26200.7623)
13th Gen Intel Core i7-1355U, 1 CPU, 12 logical and 10 physical cores
.NET SDK 10.0.103
  [Host]   : .NET 10.0.3 (10.0.326.7603), X64 RyuJIT AVX2
  ShortRun : .NET 10.0.3 (10.0.326.7603), X64 RyuJIT AVX2

Job=ShortRun  IterationCount=3  LaunchCount=1  
WarmupCount=3  

Method	N	Mean	Error	StdDev	Ratio	RatioSD	Rank	Gen0	Gen1	Gen2	Allocated	Alloc Ratio
List index access (middle)	10	0.9278 ns	1.7275 ns	0.0947 ns	0.11	0.01	1	-	-	-	-	NA
ReadOnlyCollection index access (middle)	10	0.9429 ns	1.3669 ns	0.0749 ns	0.12	0.01	2	-	-	-	-	NA
ImmutableArray index access (middle)	10	0.9507 ns	1.2508 ns	0.0686 ns	0.12	0.01	2	-	-	-	-	NA
ImmutableList index access (middle)	10	1.0329 ns	1.0362 ns	0.0568 ns	0.13	0.01	3	-	-	-	-	NA
Hashset index access (middle)	10	8.2025 ns	2.9294 ns	0.1606 ns	1.00	0.00	4	-	-	-	-	NA
ImmutableArray index access (middle)	100	0.7374 ns	0.3808 ns	0.0209 ns	0.02	0.00	1	-	-	-	-	NA
List index access (middle)	100	0.9585 ns	0.7132 ns	0.0391 ns	0.02	0.00	2	-	-	-	-	NA
ReadOnlyCollection index access (middle)	100	1.0095 ns	1.1258 ns	0.0617 ns	0.03	0.00	3	-	-	-	-	NA
ImmutableList index access (middle)	100	1.4785 ns	0.5936 ns	0.0325 ns	0.04	0.00	4	-	-	-	-	NA
Hashset index access (middle)	100	38.7006 ns	4.0684 ns	0.2230 ns	1.00	0.00	5	-	-	-	-	NA
ImmutableArray index access (middle)	1000	0.7364 ns	0.9841 ns	0.0539 ns	0.002	0.00	1	-	-	-	-	NA
List index access (middle)	1000	0.9799 ns	1.1490 ns	0.0630 ns	0.003	0.00	2	-	-	-	-	NA
ReadOnlyCollection index access (middle)	1000	0.9974 ns	0.8655 ns	0.0474 ns	0.003	0.00	3	-	-	-	-	NA
ImmutableList index access (middle)	1000	1.4309 ns	1.9841 ns	0.1088 ns	0.004	0.00	4	-	-	-	-	NA
Hashset index access (middle)	1000	353.2732 ns	70.6714 ns	3.8737 ns	1.000	0.00	5	-	-	-	-	NA
ImmutableArray index access (middle)	10000	0.7562 ns	0.6805 ns	0.0373 ns	0.000	0.00	1	-	-	-	-	NA
ReadOnlyCollection index access (middle)	10000	0.9635 ns	0.6772 ns	0.0371 ns	0.000	0.00	2	-	-	-	-	NA
List index access (middle)	10000	0.9801 ns	0.7409 ns	0.0406 ns	0.000	0.00	3	-	-	-	-	NA
ImmutableList index access (middle)	10000	1.3269 ns	0.5519 ns	0.0302 ns	0.000	0.00	4	-	-	-	-	NA
Hashset index access (middle)	10000	3,662.3615 ns	1,254.6680 ns	68.7726 ns	1.000	0.00	5	-	-	-	-	NA
Build ReadonlyDictionary from Dictionary	10	3.6705 ns	0.5668 ns	0.0311 ns	1.00	0.00	1	0.0064	-	-	40 B	1.00
Build FrozenDictionary from Dictionary	10	453.9815 ns	54.9925 ns	3.0143 ns	123.69	0.58	2	0.2151	-	-	1352 B	33.80
Build ImmutableDictionary from Dictionary	10	520.5665 ns	84.0835 ns	4.6089 ns	141.82	0.29	3	0.1287	-	-	808 B	20.20
Build ReadonlyDictionary from Dictionary	100	3.8860 ns	0.5299 ns	0.0290 ns	1.00	0.00	1	0.0064	-	-	40 B	1.00
Build FrozenDictionary from Dictionary	100	3,709.9799 ns	2,053.3477 ns	112.5509 ns	954.87	35.89	2	1.5869	0.0229	-	9968 B	249.20
Build ImmutableDictionary from Dictionary	100	6,036.0743 ns	1,318.0054 ns	72.2443 ns	1,553.42	30.00	3	1.0452	0.0229	-	6568 B	164.20
Build ReadonlyDictionary from Dictionary	1000	3.9757 ns	3.8947 ns	0.2135 ns	1.00	0.00	1	0.0064	-	-	40 B	1.00
Build FrozenDictionary from Dictionary	1000	33,232.1208 ns	10,957.4730 ns	600.6161 ns	8,371.35	367.53	2	14.4043	1.5869	-	90608 B	2,265.20
Build ImmutableDictionary from Dictionary	1000	133,669.2871 ns	7,230.8618 ns	396.3479 ns	33,690.09	1,921.84	3	10.0098	1.4648	-	64168 B	1,604.20
Build ReadonlyDictionary from Dictionary	10000	3.9717 ns	0.6569 ns	0.0360 ns	1.00	0.00	1	0.0064	-	-	40 B	1.00
Build FrozenDictionary from Dictionary	10000	516,141.3249 ns	157,767.8101 ns	8,647.7860 ns	129,949.29	1,197.26	2	173.8281	144.5313	116.2109	847003 B	21,175.08
Build ImmutableDictionary from Dictionary	10000	2,059,534.8307 ns	549,544.5574 ns	30,122.3915 ns	518,594.40	10,193.58	3	101.5625	58.5938	-	640171 B	16,004.27
List to ReadOnlyCollection	10	3.4803 ns	1.1651 ns	0.0639 ns	1.00	0.00	1	0.0038	-	-	24 B	1.00
Build ImmutableList from array	10	88.4492 ns	16.2250 ns	0.8893 ns	25.42	0.58	2	0.0802	0.0001	-	504 B	21.00
Build FrozenSet from HashSet	10	444.8004 ns	77.7502 ns	4.2617 ns	127.82	1.59	3	0.1950	-	-	1224 B	51.00
List to ReadOnlyCollection	100	3.6373 ns	1.9686 ns	0.1079 ns	1.00	0.00	1	0.0038	-	-	24 B	1.00
Build ImmutableList from array	100	802.8517 ns	110.1377 ns	6.0370 ns	220.86	6.91	2	0.7687	0.0134	-	4824 B	201.00
Build FrozenSet from HashSet	100	3,484.3878 ns	110.6370 ns	6.0644 ns	958.50	26.74	3	1.4534	0.0153	-	9120 B	380.00
List to ReadOnlyCollection	1000	3.6246 ns	2.3256 ns	0.1275 ns	1.00	0.00	1	0.0038	-	-	24 B	1.00
Build ImmutableList from array	1000	9,667.5654 ns	1,593.7098 ns	87.3566 ns	2,668.85	69.91	2	7.6447	0.9613	-	48024 B	2,001.00
Build FrozenSet from HashSet	1000	31,774.7030 ns	3,032.2156 ns	166.2060 ns	8,773.81	319.44	3	13.1226	-	-	82560 B	3,440.00
List to ReadOnlyCollection	10000	3.3767 ns	0.2402 ns	0.0132 ns	1.00	0.00	1	0.0038	-	-	24 B	1.00
Build ImmutableList from array	10000	102,208.3435 ns	9,569.1674 ns	524.5184 ns	30,269.52	231.74	2	76.4160	34.5459	-	480024 B	20,001.00
Build FrozenSet from HashSet	10000	495,070.8496 ns	69,581.8711 ns	3,814.0171 ns	146,618.42	1,506.59	3	158.2031	132.3242	113.2813	766904 B	31,954.33
FrozenSet Contains (existing)	10	1.7451 ns	0.9090 ns	0.0498 ns	0.30	0.01	1	-	-	-	-	NA
HashSet Contains (existing)	10	5.8899 ns	1.2787 ns	0.0701 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (existing)	10	6.9038 ns	1.5280 ns	0.0838 ns	1.17	0.02	3	-	-	-	-	NA
FrozenSet Contains (existing)	100	2.5355 ns	0.3187 ns	0.0175 ns	0.37	0.00	1	-	-	-	-	NA
HashSet Contains (existing)	100	6.9044 ns	0.8770 ns	0.0481 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (existing)	100	9.9141 ns	0.5886 ns	0.0323 ns	1.44	0.01	3	-	-	-	-	NA
FrozenSet Contains (existing)	1000	3.1470 ns	1.0721 ns	0.0588 ns	0.50	0.01	1	-	-	-	-	NA
HashSet Contains (existing)	1000	6.3121 ns	0.4946 ns	0.0271 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (existing)	1000	12.3377 ns	2.0079 ns	0.1101 ns	1.95	0.03	3	-	-	-	-	NA
FrozenSet Contains (existing)	10000	2.4166 ns	0.6417 ns	0.0352 ns	0.38	0.02	1	-	-	-	-	NA
HashSet Contains (existing)	10000	6.4451 ns	6.8282 ns	0.3743 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (existing)	10000	13.2918 ns	5.8766 ns	0.3221 ns	2.07	0.13	3	-	-	-	-	NA
FrozenDictionary TryGetValue (existing)	10	1.9275 ns	0.5532 ns	0.0303 ns	0.54	0.02	1	-	-	-	-	NA
ReadOnlyDictionary TryGetValue (existing)	10	3.4054 ns	0.8679 ns	0.0476 ns	0.96	0.05	2	-	-	-	-	NA
Dictionary TryGetValue (existing)	10	3.5528 ns	3.7964 ns	0.2081 ns	1.00	0.00	3	-	-	-	-	NA
ImmutableDictionary TryGetValue (existing)	10	6.1793 ns	1.5878 ns	0.0870 ns	1.74	0.09	4	-	-	-	-	NA
FrozenDictionary TryGetValue (existing)	100	2.8611 ns	0.7966 ns	0.0437 ns	0.61	0.01	1	-	-	-	-	NA
Dictionary TryGetValue (existing)	100	4.6597 ns	0.5848 ns	0.0321 ns	1.00	0.00	2	-	-	-	-	NA
ReadOnlyDictionary TryGetValue (existing)	100	5.2570 ns	2.4721 ns	0.1355 ns	1.13	0.03	3	-	-	-	-	NA
ImmutableDictionary TryGetValue (existing)	100	8.0810 ns	2.7457 ns	0.1505 ns	1.73	0.04	4	-	-	-	-	NA
FrozenDictionary TryGetValue (existing)	1000	3.7073 ns	2.3110 ns	0.1267 ns	0.92	0.03	1	-	-	-	-	NA
Dictionary TryGetValue (existing)	1000	4.0466 ns	0.8573 ns	0.0470 ns	1.00	0.00	2	-	-	-	-	NA
ReadOnlyDictionary TryGetValue (existing)	1000	4.4725 ns	1.3007 ns	0.0713 ns	1.11	0.01	3	-	-	-	-	NA
ImmutableDictionary TryGetValue (existing)	1000	9.2980 ns	2.2123 ns	0.1213 ns	2.30	0.06	4	-	-	-	-	NA
FrozenDictionary TryGetValue (existing)	10000	2.8559 ns	0.9677 ns	0.0530 ns	0.69	0.02	1	-	-	-	-	NA
Dictionary TryGetValue (existing)	10000	4.1378 ns	0.9485 ns	0.0520 ns	1.00	0.00	2	-	-	-	-	NA
ReadOnlyDictionary TryGetValue (existing)	10000	4.2453 ns	0.6164 ns	0.0338 ns	1.03	0.01	3	-	-	-	-	NA
ImmutableDictionary TryGetValue (existing)	10000	11.6684 ns	1.5330 ns	0.0840 ns	2.82	0.05	4	-	-	-	-	NA
FrozenDictionary TryGetValue (missing)	10	0.3435 ns	0.2157 ns	0.0118 ns	0.10	0.00	1	-	-	-	-	NA
Dictionary TryGetValue (missing)	10	3.5900 ns	0.8578 ns	0.0470 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableDictionary TryGetValue (missing)	10	9.7884 ns	1.3586 ns	0.0745 ns	2.73	0.02	3	-	-	-	-	NA
FrozenDictionary TryGetValue (missing)	100	0.4342 ns	0.2528 ns	0.0139 ns	0.09	0.00	1	-	-	-	-	NA
Dictionary TryGetValue (missing)	100	4.7964 ns	0.4063 ns	0.0223 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableDictionary TryGetValue (missing)	100	11.4459 ns	1.5753 ns	0.0863 ns	2.39	0.01	3	-	-	-	-	NA
FrozenDictionary TryGetValue (missing)	1000	0.3963 ns	0.6522 ns	0.0357 ns	0.11	0.01	1	-	-	-	-	NA
Dictionary TryGetValue (missing)	1000	3.7334 ns	0.7247 ns	0.0397 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableDictionary TryGetValue (missing)	1000	12.3883 ns	0.9299 ns	0.0510 ns	3.32	0.04	3	-	-	-	-	NA
FrozenDictionary TryGetValue (missing)	10000	0.5266 ns	1.0227 ns	0.0561 ns	0.13	0.01	1	-	-	-	-	NA
Dictionary TryGetValue (missing)	10000	4.0473 ns	0.4483 ns	0.0246 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableDictionary TryGetValue (missing)	10000	13.1921 ns	4.9175 ns	0.2695 ns	3.26	0.05	3	-	-	-	-	NA
FrozenSet Contains (non-existing)	10	0.9128 ns	0.1928 ns	0.0106 ns	0.19	0.00	1	-	-	-	-	NA
HashSet Contains (non-existing)	10	4.9264 ns	0.5890 ns	0.0323 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (non-existing)	10	9.3023 ns	1.8824 ns	0.1032 ns	1.89	0.03	3	-	-	-	-	NA
FrozenSet Contains (non-existing)	100	0.8450 ns	0.2892 ns	0.0159 ns	0.15	0.00	1	-	-	-	-	NA
HashSet Contains (non-existing)	100	5.8212 ns	1.9378 ns	0.1062 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (non-existing)	100	11.3568 ns	5.0529 ns	0.2770 ns	1.95	0.05	3	-	-	-	-	NA
FrozenSet Contains (non-existing)	1000	0.8135 ns	0.0605 ns	0.0033 ns	0.16	0.01	1	-	-	-	-	NA
HashSet Contains (non-existing)	1000	5.1289 ns	3.8077 ns	0.2087 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (non-existing)	1000	12.3162 ns	3.8955 ns	0.2135 ns	2.40	0.11	3	-	-	-	-	NA
FrozenSet Contains (non-existing)	10000	0.6459 ns	0.5066 ns	0.0278 ns	0.12	0.01	1	-	-	-	-	NA
HashSet Contains (non-existing)	10000	5.3123 ns	1.0285 ns	0.0564 ns	1.00	0.00	2	-	-	-	-	NA
ImmutableHashSet Contains (non-existing)	10000	13.8555 ns	2.7930 ns	0.1531 ns	2.61	0.06	3	-	-	-	-	NA
Dictionary update in-place	10	8.1697 ns	5.6596 ns	0.3102 ns	1.00	0.00	1	-	-	-	-	NA
ImmutableDictionary SetItem (creates new)	10	67.7431 ns	17.7522 ns	0.9731 ns	8.30	0.37	2	0.0370	-	-	232 B	NA
FrozenDictionary update (rebuild)	10	551.6185 ns	310.9433 ns	17.0438 ns	67.55	2.21	3	0.2928	-	-	1840 B	NA
Dictionary update in-place	100	10.9811 ns	2.4203 ns	0.1327 ns	1.00	0.00	1	-	-	-	-	NA
ImmutableDictionary SetItem (creates new)	100	112.0524 ns	15.0082 ns	0.8226 ns	10.21	0.20	2	0.0675	-	-	424 B	NA
FrozenDictionary update (rebuild)	100	4,029.6183 ns	681.7027 ns	37.3664 ns	367.02	7.26	3	2.0905	0.0305	-	13144 B	NA
Dictionary update in-place	1000	9.6840 ns	2.5193 ns	0.1381 ns	1.00	0.00	1	-	-	-	-	NA
ImmutableDictionary SetItem (creates new)	1000	164.4658 ns	27.2139 ns	1.4917 ns	16.99	0.28	2	0.0980	-	-	616 B	NA
FrozenDictionary update (rebuild)	1000	37,609.2306 ns	4,652.2680 ns	255.0065 ns	3,883.91	28.83	3	19.3481	2.1362	-	121672 B	NA
Dictionary update in-place	10000	9.7677 ns	1.5672 ns	0.0859 ns	1.00	0.00	1	-	-	-	-	NA
ImmutableDictionary SetItem (creates new)	10000	213.5151 ns	17.4067 ns	0.9541 ns	21.86	0.09	2	0.1287	-	-	808 B	NA
FrozenDictionary update (rebuild)	10000	605,496.2891 ns	333,162.0393 ns	18,261.7356 ns	61,989.69	1,767.68	3	230.4688	195.3125	166.0156	1130445 B	NA

ReadonlyVsImmutableVsFrozen.cs

[MemoryDiagnoser]
[Orderer(SummaryOrderPolicy.FastestToSlowest)]
[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
[RankColumn]
[ShortRunJob]
[KeepBenchmarkFiles]
[HtmlExporter]
[MarkdownExporterAttribute.Default]
[MarkdownExporterAttribute.GitHub]
public class ReadonlyVsImmutableVsFrozen
{
    //[Params(10, 12)]
    [Params(10, 100, 1_000, 10_000)]
    public int N;

    private string[] _gameNames = default!;

    // List-ish
    private List<string> _list = default!;
    private ReadOnlyCollection<string> _readOnlyCollection = default!;
    private IReadOnlyList<string> _iReadOnlyList = default!;
    private ImmutableArray<string> _immutableArray;
    private ImmutableList<string> _immutableList = default!;

    // Set-ish
    private HashSet<string> _hashSet = default!;
    private ImmutableHashSet<string> _immutableHashSet = default!;
    private FrozenSet<string> _frozenSet = default!;

    // Dictionary-ish: "game -> BGG weight-ish score"
    private Dictionary<string, int> _dict = default!;
    private ReadOnlyDictionary<string, int> _readOnlyDict = default!;
    private ImmutableDictionary<string, int> _immutableDict = default!;
    private FrozenDictionary<string, int> _frozenDict = default!;

    private string _existingKey = default!;
    private string _missingKey = default!;

    [GlobalSetup]
    public void Setup()
    {
        _gameNames = new string[N];
        for (int i = 0; i < N; i++)
            _gameNames[i] = $"Game-{i:000000}";

        _existingKey = _gameNames[N / 2];
        _missingKey = "Game-DOES-NOT-EXIST";

        // List-ish
        _list = new List<string>(_gameNames);
        _readOnlyCollection = _list.AsReadOnly();
        _iReadOnlyList = _readOnlyCollection; // same underlying wrapper
        _immutableArray = ImmutableArray.Create(_gameNames);
        _immutableList = ImmutableList.Create(_gameNames);

        // Set-ish
        _hashSet = new HashSet<string>(_gameNames, StringComparer.Ordinal);
        _immutableHashSet = _hashSet.ToImmutableHashSet(StringComparer.Ordinal);
        _frozenSet = _hashSet.ToFrozenSet(StringComparer.Ordinal);

        // Dictionary-ish
        _dict = new Dictionary<string, int>(N, StringComparer.Ordinal);
        for (int i = 0; i < N; i++)
            _dict[_gameNames[i]] = (i % 5) + 1; // 1..5

        _readOnlyDict = new ReadOnlyDictionary<string, int>(_dict);
        _immutableDict = _dict.ToImmutableDictionary(StringComparer.Ordinal);
        _frozenDict = _dict.ToFrozenDictionary(StringComparer.Ordinal);

    }

    // -------------------------
    // Build cost (one-time)
    // -------------------------


    #region Creation of collection
    [Benchmark(Description = "List to ReadOnlyCollection", Baseline = true)
        , BenchmarkCategory("Creation of collection")]
    public ReadOnlyCollection<string> Build_ReadOnlyCollection()
        => _list.AsReadOnly();

    [Benchmark(Description = "Build ImmutableList from array")
        , BenchmarkCategory("Creation of collection")]
    public ImmutableList<string> Build_ImmutableList()
        => ImmutableList.Create(_gameNames);

    [Benchmark(Description = "Build FrozenSet from HashSet")
        , BenchmarkCategory("Creation of collection")]
    public FrozenSet<string> Build_FrozenSet()
        => _hashSet.ToFrozenSet(StringComparer.Ordinal);

    #endregion

    #region Creation of Dictionary

    [Benchmark(Description = "Build ReadonlyDictionary from Dictionary", Baseline =true),
     BenchmarkCategory("Creation of Dictionary")]
    public ReadOnlyDictionary<string, int> Build_ReadOnlyDictionary()
        => new ReadOnlyDictionary<string, int>(_dict);

    [Benchmark(Description = "Build ImmutableDictionary from Dictionary"),
      BenchmarkCategory("Creation of Dictionary")]
    public ImmutableDictionary<string, int> Build_ImmutableDictionary()
      => _dict.ToImmutableDictionary(StringComparer.Ordinal);

    [Benchmark(Description = "Build FrozenDictionary from Dictionary")
        , BenchmarkCategory("Creation of Dictionary")]
    public FrozenDictionary<string, int> Build_FrozenDictionary()
        => _dict.ToFrozenDictionary(StringComparer.Ordinal);
    #endregion

    // -------------------------
    // Read performance
    // -------------------------

    #region Access by index
    [Benchmark(Description = "List index access (middle)")
        , BenchmarkCategory("Access by index")]
    public string Read_List_Index()
        => _list[N / 2];

    [Benchmark(Description = "ReadOnlyCollection index access (middle)")
        , BenchmarkCategory("Access by index")]
    public string Read_ReadOnlyCollection_Index()
        => _readOnlyCollection[N / 2];

    [Benchmark(Description = "ImmutableArray index access (middle)")
        , BenchmarkCategory("Access by index")]
    public string Read_ImmutableArray_Index()
        => _immutableArray[N / 2];

    [Benchmark(Description = "ImmutableList index access (middle)")
        , BenchmarkCategory("Access by index")]
    public string Read_ImmutableList_Index()
        => _immutableList[N / 2];


    [Benchmark(Description = "Hashset index access (middle)", Baseline =true)
        , BenchmarkCategory("Access by index")]
    public string Read_HashSet_Index()
        => _hashSet.ElementAt(N / 2);

    #endregion Access by index

    #region Contains  existing key

    [Benchmark(Description = "HashSet Contains (existing)", Baseline =true)
        , BenchmarkCategory("Search existing key")]
    public bool Read_HashSet_Contains_Existing()
        => _hashSet.Contains(_existingKey);

    [Benchmark(Description = "ImmutableHashSet Contains (existing)")
         , BenchmarkCategory("Search existing key")]
    public bool Read_ImmutableHashSet_Contains_Existing()
        => _immutableHashSet.Contains(_existingKey);

    [Benchmark(Description = "FrozenSet Contains (existing)")
        , BenchmarkCategory("Search existing key")]
    public bool Read_FrozenSet_Contains_Existing()
        => _frozenSet.Contains(_existingKey);

    #endregion

    #region Contains non existing key

    [Benchmark(Description = "HashSet Contains (non-existing)", Baseline = true)
        , BenchmarkCategory("Search non-existing key")]
    public bool Read_HashSet_Contains_NonExisting()
        => _hashSet.Contains(_missingKey);

    [Benchmark(Description = "ImmutableHashSet Contains (non-existing)")
         , BenchmarkCategory("Search non-existing key")]
    public bool Read_ImmutableHashSet_Contains_NonExisting()
        => _immutableHashSet.Contains(_missingKey);

    [Benchmark(Description = "FrozenSet Contains (non-existing)")
        , BenchmarkCategory("Search non-existing key")]
    public bool Read_FrozenSet_Contains_NonExisting()
        => _frozenSet.Contains(_missingKey);

    #endregion

    #region Search existing key in dictionary

    [Benchmark(Description = "Dictionary TryGetValue (existing)", Baseline =true)
        , BenchmarkCategory("Search existing key in dictionary")]
    public int Read_Dictionary_TryGetValue_Existing()
        => _dict.TryGetValue(_existingKey, out var v) ? v : 0;

    [Benchmark(Description = "ReadOnlyDictionary TryGetValue (existing)")
        , BenchmarkCategory("Search existing key in dictionary")]
    public int Read_ReadOnlyDictionary_TryGetValue_Existing()
        => _readOnlyDict.TryGetValue(_existingKey, out var v) ? v : 0;

    [Benchmark(Description = "ImmutableDictionary TryGetValue (existing)")
        , BenchmarkCategory("Search existing key in dictionary")]
    public int Read_ImmutableDictionary_TryGetValue_Existing()
        => _immutableDict.TryGetValue(_existingKey, out var v) ? v : 0;

    [Benchmark(Description = "FrozenDictionary TryGetValue (existing)")
        , BenchmarkCategory("Search existing key in dictionary")]
    public int Read_FrozenDictionary_TryGetValue_Existing()
        => _frozenDict.TryGetValue(_existingKey, out var v) ? v : 0;
    #endregion
    // -------------------------
    // Miss performance (lookup negative case)
    // -------------------------

    [Benchmark(Description = "Dictionary TryGetValue (missing)", Baseline = true)
        , BenchmarkCategory("Search missing key")]
    public int Read_Dictionary_TryGetValue_Missing()
        => _dict.TryGetValue(_missingKey, out var v) ? v : 0;

    [Benchmark(Description = "ImmutableDictionary TryGetValue (missing)")
        , BenchmarkCategory("Search missing key")]
    public int Read_ImmutableDictionary_TryGetValue_Missing()
        => _immutableDict.TryGetValue(_missingKey, out var v) ? v : 0;

    [Benchmark(Description = "FrozenDictionary TryGetValue (missing)")
        , BenchmarkCategory("Search missing key")]
    public int Read_FrozenDictionary_TryGetValue_Missing()
        => _frozenDict.TryGetValue(_missingKey, out var v) ? v : 0;

    // -------------------------
    // Update behavior examples
    // -------------------------

    [Benchmark(Description = "ImmutableDictionary SetItem (creates new)")
        , BenchmarkCategory("Update")]
    public ImmutableDictionary<string, int> Update_ImmutableDictionary_SetItem()
        => _immutableDict.SetItem(_existingKey, 99);

    [Benchmark(Description = "Dictionary update in-place", Baseline =true)
        , BenchmarkCategory("Update")]
    public int Update_Dictionary_InPlace()
    {
        _dict[_existingKey] = 99;
        return _dict[_existingKey];
    }

    // Frozen update requires rebuild; this benchmark shows the cost explicitly.
    [Benchmark(Description = "FrozenDictionary 'update' (rebuild)")
        , BenchmarkCategory("Update")]
    public FrozenDictionary<string, int> Update_FrozenDictionary_Rebuild()
    {
        var copy = new Dictionary<string, int>(_dict, StringComparer.Ordinal)
        {
            [_existingKey] = 99
        };
        return copy.ToFrozenDictionary(StringComparer.Ordinal);
    }
}