• Stars
    star
    224
  • Rank 177,792 (Top 4 %)
  • Language
    C#
  • License
    MIT License
  • Created almost 8 years ago
  • Updated 3 months ago

Reviews

There are no reviews yet. Be the first to send feedback to the community and the maintainers!

Repository Details

Fast and memory-efficient immutable collections and helper data structures

ImTools

license

  • Windows, Linux, MacOS CI build
  • Lib package NuGet Badge
  • Code package NuGet Badge
  • Latest release latest release

Fast and memory-efficient immutable collections and helper data structures.

Split from the DryIoc.

Benchmarks

The comparison is done against the previous versions and the variety of BCL C# collections including the experimental Microsoft.Collections.Extensions.DictionarySlim<K, V>.

Important: Keep in mind that immutable collections have a different use-case and a thread-safety guarantees compared to the Dictionary, DictionarySlim or even ConcurrentDictionary. The closest comparable would be the ImmutableDictionary. The benchmarks do not take the collections "nature" into account and run through the simplest available API path.

ImHashMap of Type keys and small string values

Population

The benchmark inserts from 10 to 1000 items into the ImHashMap<Type, string>:

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                            Method | Count |          Mean |        Error |       StdDev | Ratio | RatioSD |    Gen 0 |   Gen 1 | Gen 2 | Allocated |
|---------------------------------- |------ |--------------:|-------------:|-------------:|------:|--------:|---------:|--------:|------:|----------:|
|          V4_ImHashMap_AddOrUpdate |     1 |      33.32 ns |     0.439 ns |     0.389 ns |  1.00 |    0.00 |   0.0178 |       - |     - |     112 B |
|          V3_ImHashMap_AddOrUpdate |     1 |      35.97 ns |     0.639 ns |     0.567 ns |  1.08 |    0.02 |   0.0178 |       - |     - |     112 B |
| V4_PartitionedHashMap_AddOrUpdate |     1 |      97.72 ns |     1.294 ns |     1.148 ns |  2.93 |    0.05 |   0.0370 |       - |     - |     232 B |
|                   DictSlim_TryAdd |     1 |      59.37 ns |     0.519 ns |     0.434 ns |  1.78 |    0.02 |   0.0229 |       - |     - |     144 B |
|                       Dict_TryAdd |     1 |      65.94 ns |     0.631 ns |     0.560 ns |  1.98 |    0.02 |   0.0343 |       - |     - |     216 B |
|       ConcurrentDictionary_TryAdd |     1 |     197.29 ns |     1.883 ns |     1.761 ns |  5.92 |    0.09 |   0.1466 |  0.0007 |     - |     920 B |
|         ImmutableDict_Builder_Add |     1 |     220.79 ns |     2.648 ns |     2.477 ns |  6.62 |    0.10 |   0.0355 |       - |     - |     224 B |
|                 ImmutableDict_Add |     1 |     264.15 ns |     4.786 ns |     3.737 ns |  7.93 |    0.16 |   0.0429 |       - |     - |     272 B |
|                                   |       |               |              |              |       |         |          |         |       |           |
|          V4_ImHashMap_AddOrUpdate |    10 |     307.91 ns |     5.281 ns |     4.940 ns |  1.00 |    0.00 |   0.1564 |  0.0005 |     - |     984 B |
|          V3_ImHashMap_AddOrUpdate |    10 |     389.09 ns |     6.482 ns |     5.746 ns |  1.27 |    0.03 |   0.1593 |  0.0005 |     - |    1000 B |
| V4_PartitionedHashMap_AddOrUpdate |    10 |     392.47 ns |     4.296 ns |     5.276 ns |  1.27 |    0.03 |   0.1144 |  0.0005 |     - |     720 B |
|                   DictSlim_TryAdd |    10 |     409.45 ns |     2.216 ns |     1.965 ns |  1.33 |    0.02 |   0.1707 |  0.0005 |     - |    1072 B |
|                       Dict_TryAdd |    10 |     413.38 ns |     5.460 ns |     5.107 ns |  1.34 |    0.03 |   0.1578 |  0.0005 |     - |     992 B |
|       ConcurrentDictionary_TryAdd |    10 |   1,319.88 ns |    20.332 ns |    19.019 ns |  4.29 |    0.11 |   0.4730 |  0.0076 |     - |    2968 B |
|         ImmutableDict_Builder_Add |    10 |   1,712.26 ns |    15.264 ns |    26.733 ns |  5.59 |    0.12 |   0.1259 |       - |     - |     800 B |
|                 ImmutableDict_Add |    10 |   2,986.38 ns |    17.824 ns |    14.884 ns |  9.70 |    0.18 |   0.4349 |       - |     - |    2744 B |
|                                   |       |               |              |              |       |         |          |         |       |           |
|          V4_ImHashMap_AddOrUpdate |   100 |   9,188.79 ns |   116.272 ns |   108.761 ns |  1.00 |    0.00 |   2.8229 |  0.0916 |     - |   17792 B |
|          V3_ImHashMap_AddOrUpdate |   100 |  10,591.30 ns |   169.894 ns |   141.869 ns |  1.15 |    0.03 |   3.1891 |  0.1068 |     - |   20032 B |
| V4_PartitionedHashMap_AddOrUpdate |   100 |   4,491.75 ns |    81.205 ns |    75.959 ns |  0.49 |    0.01 |   1.2360 |  0.0534 |     - |    7776 B |
|                   DictSlim_TryAdd |   100 |   3,201.77 ns |    48.216 ns |    42.743 ns |  0.35 |    0.01 |   1.1902 |  0.0305 |     - |    7488 B |
|                       Dict_TryAdd |   100 |   3,856.61 ns |    70.806 ns |    62.768 ns |  0.42 |    0.01 |   1.6174 |  0.0687 |     - |   10192 B |
|       ConcurrentDictionary_TryAdd |   100 |  16,035.70 ns |   320.350 ns |   356.068 ns |  1.75 |    0.04 |   4.9133 |  0.5798 |     - |   30824 B |
|         ImmutableDict_Builder_Add |   100 |  24,427.83 ns |   470.630 ns |   417.201 ns |  2.66 |    0.07 |   1.0376 |  0.0305 |     - |    6560 B |
|                 ImmutableDict_Add |   100 |  48,772.32 ns |   687.894 ns |   574.422 ns |  5.30 |    0.10 |   7.1411 |  0.2441 |     - |   44936 B |
|                                   |       |               |              |              |       |         |          |         |       |           |
|          V4_ImHashMap_AddOrUpdate |  1000 | 277,024.17 ns | 3,349.815 ns | 2,969.524 ns |  1.00 |    0.00 |  45.4102 | 10.7422 |     - |  286344 B |
|          V3_ImHashMap_AddOrUpdate |  1000 | 234,444.41 ns | 2,324.332 ns | 1,940.923 ns |  0.85 |    0.01 |  51.5137 | 12.2070 |     - |  324176 B |
| V4_PartitionedHashMap_AddOrUpdate |  1000 | 146,984.47 ns |   954.053 ns |   845.743 ns |  0.53 |    0.01 |  26.1230 |  7.5684 |     - |  164280 B |
|                   DictSlim_TryAdd |  1000 |  33,447.54 ns |   254.743 ns |   225.823 ns |  0.12 |    0.00 |   9.1553 |  1.7700 |     - |   57808 B |
|                       Dict_TryAdd |  1000 |  40,234.23 ns |   430.048 ns |   381.226 ns |  0.15 |    0.00 |  16.2354 |  5.3711 |     - |  102216 B |
|       ConcurrentDictionary_TryAdd |  1000 | 165,018.54 ns | 3,075.862 ns | 2,568.484 ns |  0.60 |    0.01 |  41.2598 | 13.6719 |     - |  259720 B |
|         ImmutableDict_Builder_Add |  1000 | 396,623.48 ns | 4,099.094 ns | 3,834.295 ns |  1.43 |    0.02 |   9.7656 |  2.4414 |     - |   64160 B |
|                 ImmutableDict_Add |  1000 | 813,397.08 ns | 9,203.453 ns | 8,608.916 ns |  2.94 |    0.04 | 105.4688 | 25.3906 |     - |  665001 B |

Lookup

The benchmark lookups for the specific key in the ImHashMap<Type, string> containing the specified Count of elements.

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                           Method | Count |      Mean |     Error |    StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|--------------------------------- |------ |----------:|----------:|----------:|------:|--------:|------:|------:|------:|----------:|
|             V4_ImHashMap_TryFind |     1 |  8.915 ns | 0.1853 ns | 0.1733 ns |  1.00 |    0.00 |     - |     - |     - |         - |
|             V3_ImHashMap_TryFind |     1 |  7.834 ns | 0.1769 ns | 0.1568 ns |  0.88 |    0.02 |     - |     - |     - |         - |
|    V4_PartitionedHashMap_TryFind |     1 |  8.292 ns | 0.1082 ns | 0.0959 ns |  0.93 |    0.02 |     - |     - |     - |         - |
|    V3_PartitionedHashMap_TryFind |     1 |  7.681 ns | 0.1245 ns | 0.1039 ns |  0.86 |    0.02 |     - |     - |     - |         - |
|       DictionarySlim_TryGetValue |     1 |  8.861 ns | 0.1423 ns | 0.1188 ns |  0.99 |    0.02 |     - |     - |     - |         - |
|           Dictionary_TryGetValue |     1 | 17.914 ns | 0.3447 ns | 0.3055 ns |  2.01 |    0.05 |     - |     - |     - |         - |
| ConcurrentDictionary_TryGetValue |     1 | 13.381 ns | 0.2709 ns | 0.2401 ns |  1.50 |    0.04 |     - |     - |     - |         - |
|             ImmutableDict_TryGet |     1 | 19.040 ns | 0.3068 ns | 0.2870 ns |  2.14 |    0.06 |     - |     - |     - |         - |
|                                  |       |           |           |           |       |         |       |       |       |           |
|             V4_ImHashMap_TryFind |    10 |  9.462 ns | 0.2690 ns | 0.2246 ns |  1.00 |    0.00 |     - |     - |     - |         - |
|             V3_ImHashMap_TryFind |    10 |  9.038 ns | 0.1650 ns | 0.1463 ns |  0.96 |    0.02 |     - |     - |     - |         - |
|    V4_PartitionedHashMap_TryFind |    10 |  8.575 ns | 0.2031 ns | 0.1900 ns |  0.91 |    0.03 |     - |     - |     - |         - |
|    V3_PartitionedHashMap_TryFind |    10 |  5.869 ns | 0.1026 ns | 0.1743 ns |  0.63 |    0.02 |     - |     - |     - |         - |
|       DictionarySlim_TryGetValue |    10 |  7.384 ns | 0.1882 ns | 0.1668 ns |  0.78 |    0.03 |     - |     - |     - |         - |
|           Dictionary_TryGetValue |    10 | 14.082 ns | 0.2168 ns | 0.1921 ns |  1.49 |    0.04 |     - |     - |     - |         - |
| ConcurrentDictionary_TryGetValue |    10 | 11.436 ns | 0.1398 ns | 0.1239 ns |  1.21 |    0.03 |     - |     - |     - |         - |
|             ImmutableDict_TryGet |    10 | 17.927 ns | 0.4467 ns | 0.4780 ns |  1.90 |    0.09 |     - |     - |     - |         - |
|                                  |       |           |           |           |       |         |       |       |       |           |
|             V4_ImHashMap_TryFind |   100 | 12.147 ns | 0.1475 ns | 0.1308 ns |  1.00 |    0.00 |     - |     - |     - |         - |
|             V3_ImHashMap_TryFind |   100 | 11.357 ns | 0.1695 ns | 0.1323 ns |  0.94 |    0.01 |     - |     - |     - |         - |
|    V4_PartitionedHashMap_TryFind |   100 |  8.520 ns | 0.2142 ns | 0.1899 ns |  0.70 |    0.02 |     - |     - |     - |         - |
|    V3_PartitionedHashMap_TryFind |   100 |  7.785 ns | 0.1374 ns | 0.1147 ns |  0.64 |    0.01 |     - |     - |     - |         - |
|       DictionarySlim_TryGetValue |   100 |  6.918 ns | 0.1544 ns | 0.1289 ns |  0.57 |    0.01 |     - |     - |     - |         - |
|           Dictionary_TryGetValue |   100 | 13.804 ns | 0.3474 ns | 0.3717 ns |  1.14 |    0.04 |     - |     - |     - |         - |
| ConcurrentDictionary_TryGetValue |   100 | 11.432 ns | 0.2194 ns | 0.2052 ns |  0.94 |    0.02 |     - |     - |     - |         - |
|             ImmutableDict_TryGet |   100 | 21.593 ns | 0.4048 ns | 0.3786 ns |  1.78 |    0.03 |     - |     - |     - |         - |
|                                  |       |           |           |           |       |         |       |       |       |           |
|             V4_ImHashMap_TryFind |  1000 | 15.492 ns | 0.3859 ns | 0.4881 ns |  1.00 |    0.00 |     - |     - |     - |         - |
|             V3_ImHashMap_TryFind |  1000 | 14.339 ns | 0.2612 ns | 0.2444 ns |  0.92 |    0.03 |     - |     - |     - |         - |
|    V4_PartitionedHashMap_TryFind |  1000 | 11.508 ns | 0.1839 ns | 0.1630 ns |  0.74 |    0.03 |     - |     - |     - |         - |
|    V3_PartitionedHashMap_TryFind |  1000 |  9.508 ns | 0.2340 ns | 0.2074 ns |  0.61 |    0.02 |     - |     - |     - |         - |
|       DictionarySlim_TryGetValue |  1000 |  7.099 ns | 0.1984 ns | 0.2037 ns |  0.46 |    0.01 |     - |     - |     - |         - |
|           Dictionary_TryGetValue |  1000 | 13.696 ns | 0.1341 ns | 0.1120 ns |  0.88 |    0.03 |     - |     - |     - |         - |
| ConcurrentDictionary_TryGetValue |  1000 | 11.358 ns | 0.1464 ns | 0.1222 ns |  0.73 |    0.03 |     - |     - |     - |         - |
|             ImmutableDict_TryGet |  1000 | 25.875 ns | 0.3752 ns | 0.3510 ns |  1.67 |    0.06 |     - |     - |     - |         - |

Enumeration

The benchmark source

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                          Method | Count |         Mean |      Error |     StdDev |       Median | Ratio | RatioSD |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|-------------------------------- |------ |-------------:|-----------:|-----------:|-------------:|------:|--------:|-------:|------:|------:|----------:|
|          V4_ImHashMap_Enumerate |     1 |     39.51 ns |   0.865 ns |   0.996 ns |     39.43 ns |  1.00 |    0.00 |      - |     - |     - |         - |
|          V3_ImHashMap_Enumerate |     1 |     44.11 ns |   0.879 ns |   0.822 ns |     44.28 ns |  1.12 |    0.04 | 0.0255 |     - |     - |     160 B |
| V4_PartitionedHashMap_Enumerate |     1 |    118.94 ns |   1.644 ns |   1.538 ns |    118.91 ns |  3.01 |    0.09 |      - |     - |     - |         - |
| V3_PartitionedHashMap_Enumerate |     1 |    180.82 ns |   3.462 ns |   3.238 ns |    181.09 ns |  4.57 |    0.14 | 0.0522 |     - |     - |     328 B |
|        DictionarySlim_Enumerate |     1 |     12.77 ns |   0.254 ns |   0.238 ns |     12.76 ns |  0.32 |    0.01 |      - |     - |     - |         - |
|            Dictionary_Enumerate |     1 |     15.24 ns |   0.652 ns |   1.817 ns |     14.36 ns |  0.46 |    0.05 |      - |     - |     - |         - |
|    ConcurrentDictionary_foreach |     1 |    177.04 ns |   2.073 ns |   1.939 ns |    176.68 ns |  4.47 |    0.12 | 0.0100 |     - |     - |      64 B |
|         ImmutableDict_Enumerate |     1 |    161.96 ns |   0.760 ns |   0.635 ns |    161.98 ns |  4.08 |    0.12 |      - |     - |     - |         - |
|                                 |       |              |            |            |              |       |         |        |       |       |           |
|          V4_ImHashMap_Enumerate |    10 |    191.91 ns |   3.010 ns |   2.668 ns |    192.57 ns |  1.00 |    0.00 |      - |     - |     - |         - |
|          V3_ImHashMap_Enumerate |    10 |    223.10 ns |   1.885 ns |   1.574 ns |    223.12 ns |  1.16 |    0.02 | 0.0381 |     - |     - |     240 B |
| V4_PartitionedHashMap_Enumerate |    10 |    379.75 ns |   4.543 ns |   4.027 ns |    379.74 ns |  1.98 |    0.03 |      - |     - |     - |         - |
| V3_PartitionedHashMap_Enumerate |    10 |    604.47 ns |   4.257 ns |   3.774 ns |    603.87 ns |  3.15 |    0.05 | 0.1793 |     - |     - |    1128 B |
|        DictionarySlim_Enumerate |    10 |     73.15 ns |   1.438 ns |   1.345 ns |     72.82 ns |  0.38 |    0.01 |      - |     - |     - |         - |
|            Dictionary_Enumerate |    10 |     57.95 ns |   0.749 ns |   0.701 ns |     57.86 ns |  0.30 |    0.01 |      - |     - |     - |         - |
|    ConcurrentDictionary_foreach |    10 |    505.36 ns |   7.959 ns |   7.445 ns |    504.00 ns |  2.64 |    0.05 | 0.0095 |     - |     - |      64 B |
|         ImmutableDict_Enumerate |    10 |    556.35 ns |  10.730 ns |   9.512 ns |    558.53 ns |  2.90 |    0.06 |      - |     - |     - |         - |
|                                 |       |              |            |            |              |       |         |        |       |       |           |
|          V4_ImHashMap_Enumerate |   100 |  2,023.65 ns |  33.506 ns |  29.702 ns |  2,031.78 ns |  1.00 |    0.00 |      - |     - |     - |         - |
|          V3_ImHashMap_Enumerate |   100 |  1,992.46 ns |  23.400 ns |  20.744 ns |  1,992.05 ns |  0.98 |    0.02 | 0.0381 |     - |     - |     240 B |
| V4_PartitionedHashMap_Enumerate |   100 |  2,626.85 ns |  42.089 ns |  37.311 ns |  2,616.34 ns |  1.30 |    0.02 |      - |     - |     - |         - |
| V3_PartitionedHashMap_Enumerate |   100 |  3,469.16 ns |  30.415 ns |  26.962 ns |  3,469.32 ns |  1.71 |    0.03 | 0.4349 |     - |     - |    2728 B |
|        DictionarySlim_Enumerate |   100 |    615.29 ns |  10.217 ns |   9.057 ns |    617.89 ns |  0.30 |    0.01 |      - |     - |     - |         - |
|            Dictionary_Enumerate |   100 |    578.30 ns |   3.310 ns |   2.764 ns |    578.14 ns |  0.29 |    0.00 |      - |     - |     - |         - |
|    ConcurrentDictionary_foreach |   100 |  3,444.60 ns |  55.779 ns |  52.176 ns |  3,425.75 ns |  1.70 |    0.03 | 0.0076 |     - |     - |      64 B |
|         ImmutableDict_Enumerate |   100 |  4,557.81 ns |  71.187 ns |  63.105 ns |  4,552.69 ns |  2.25 |    0.03 |      - |     - |     - |         - |
|                                 |       |              |            |            |              |       |         |        |       |       |           |
|          V4_ImHashMap_Enumerate |  1000 | 22,259.46 ns | 204.173 ns | 180.994 ns | 22,241.67 ns |  1.00 |    0.00 |      - |     - |     - |         - |
|          V3_ImHashMap_Enumerate |  1000 | 21,710.99 ns | 288.512 ns | 240.921 ns | 21,770.78 ns |  0.98 |    0.02 | 0.0610 |     - |     - |     480 B |
| V4_PartitionedHashMap_Enumerate |  1000 | 28,097.70 ns | 392.513 ns | 306.449 ns | 28,134.91 ns |  1.26 |    0.02 |      - |     - |     - |         - |
| V3_PartitionedHashMap_Enumerate |  1000 | 31,132.68 ns | 473.705 ns | 443.104 ns | 31,208.71 ns |  1.40 |    0.01 | 0.4272 |     - |     - |    2728 B |
|        DictionarySlim_Enumerate |  1000 |  6,472.19 ns |  53.546 ns |  47.467 ns |  6,482.73 ns |  0.29 |    0.00 |      - |     - |     - |         - |
|            Dictionary_Enumerate |  1000 |  5,700.68 ns |  65.696 ns |  61.452 ns |  5,698.15 ns |  0.26 |    0.00 |      - |     - |     - |         - |
|    ConcurrentDictionary_foreach |  1000 | 43,550.74 ns | 848.746 ns | 752.391 ns | 43,765.79 ns |  1.96 |    0.04 |      - |     - |     - |      64 B |
|         ImmutableDict_Enumerate |  1000 | 46,089.57 ns | 524.157 ns | 464.651 ns | 46,183.41 ns |  2.07 |    0.03 |      - |     - |     - |         - |

ImHashMap with int keys and small string values

ImHashMap<int, string> stores the int keys and string values.

Population

The benchmark inserts from 1 to 10 000 of items into the ImHashMap<int, string>:

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                          Method | Count |             Mean |          Error |         StdDev |           Median | Ratio | RatioSD |     Gen 0 |    Gen 1 |    Gen 2 | Allocated |
|-------------------------------- |------ |-----------------:|---------------:|---------------:|-----------------:|------:|--------:|----------:|---------:|---------:|----------:|
|        V4_ImHashMap_AddOrUpdate |     1 |         13.30 ns |       0.296 ns |       0.277 ns |         13.30 ns |  1.00 |    0.00 |    0.0051 |        - |        - |      32 B |
|            V2_ImMap_AddOrUpdate |     1 |         17.09 ns |       0.207 ns |       0.184 ns |         17.08 ns |  1.28 |    0.03 |    0.0076 |        - |        - |      48 B |
| V4_PartitionedImMap_AddOrUpdate |     1 |         79.98 ns |       1.023 ns |       1.467 ns |         79.66 ns |  6.04 |    0.16 |    0.0293 |        - |        - |     184 B |
|       DictSlim_GetOrAddValueRef |     1 |         41.18 ns |       0.416 ns |       0.369 ns |         41.28 ns |  3.10 |    0.08 |    0.0204 |        - |        - |     128 B |
|                     Dict_TryAdd |     1 |         37.06 ns |       0.418 ns |       0.370 ns |         37.08 ns |  2.79 |    0.06 |    0.0344 |        - |        - |     216 B |
|           ConcurrentDict_TryAdd |     1 |        146.05 ns |       2.124 ns |       1.773 ns |        145.64 ns | 10.95 |    0.27 |    0.1376 |   0.0007 |        - |     864 B |
|       ImmutableDict_Builder_Add |     1 |        120.60 ns |       0.788 ns |       0.658 ns |        120.43 ns |  9.05 |    0.20 |    0.0253 |        - |        - |     160 B |
|               ImmutableDict_Add |     1 |        107.37 ns |       1.833 ns |       2.384 ns |        106.71 ns |  8.11 |    0.25 |    0.0166 |        - |        - |     104 B |
|                                 |       |                  |                |                |                  |       |         |           |          |          |           |
|        V4_ImHashMap_AddOrUpdate |    10 |        229.89 ns |       1.484 ns |       1.239 ns |        230.08 ns |  1.00 |    0.00 |    0.1173 |        - |        - |     736 B |
|            V2_ImMap_AddOrUpdate |    10 |        551.17 ns |       4.425 ns |       3.695 ns |        550.33 ns |  2.40 |    0.02 |    0.2823 |        - |        - |    1776 B |
| V4_PartitionedImMap_AddOrUpdate |    10 |        242.93 ns |       4.599 ns |       3.840 ns |        242.93 ns |  1.06 |    0.02 |    0.0749 |        - |        - |     472 B |
|       DictSlim_GetOrAddValueRef |    10 |        281.33 ns |       5.547 ns |       5.935 ns |        280.41 ns |  1.22 |    0.03 |    0.1326 |        - |        - |     832 B |
|                     Dict_TryAdd |    10 |        258.89 ns |       3.412 ns |       3.025 ns |        258.85 ns |  1.13 |    0.01 |    0.1578 |   0.0005 |        - |     992 B |
|           ConcurrentDict_TryAdd |    10 |        540.34 ns |       3.092 ns |       2.741 ns |        539.06 ns |  2.35 |    0.01 |    0.1945 |   0.0010 |        - |    1224 B |
|       ImmutableDict_Builder_Add |    10 |      1,514.60 ns |       8.675 ns |       7.244 ns |      1,513.34 ns |  6.59 |    0.05 |    0.1163 |        - |        - |     736 B |
|               ImmutableDict_Add |    10 |      2,632.30 ns |      51.955 ns |      48.599 ns |      2,639.68 ns | 11.45 |    0.22 |    0.4196 |        - |        - |    2640 B |
|                                 |       |                  |                |                |                  |       |         |           |          |          |           |
|        V4_ImHashMap_AddOrUpdate |   100 |      8,221.37 ns |     125.831 ns |     117.703 ns |      8,192.32 ns |  1.00 |    0.00 |    2.9602 |   0.1221 |        - |   18640 B |
|            V2_ImMap_AddOrUpdate |   100 |     12,184.44 ns |     179.889 ns |     168.268 ns |     12,140.26 ns |  1.48 |    0.02 |    5.9357 |   0.2441 |        - |   37296 B |
| V4_PartitionedImMap_AddOrUpdate |   100 |      3,370.45 ns |      23.906 ns |      18.664 ns |      3,363.21 ns |  0.41 |    0.01 |    1.4801 |   0.0839 |        - |    9304 B |
|       DictSlim_GetOrAddValueRef |   100 |      2,652.96 ns |      37.693 ns |      35.258 ns |      2,649.32 ns |  0.32 |    0.00 |    1.3275 |   0.0534 |        - |    8336 B |
|                     Dict_TryAdd |   100 |      2,828.22 ns |      21.898 ns |      19.412 ns |      2,826.77 ns |  0.34 |    0.01 |    2.0828 |   0.1297 |        - |   13072 B |
|           ConcurrentDict_TryAdd |   100 |     10,866.25 ns |     111.428 ns |     104.229 ns |     10,909.92 ns |  1.32 |    0.02 |    3.6316 |   0.3510 |        - |   22784 B |
|       ImmutableDict_Builder_Add |   100 |     25,598.91 ns |     273.166 ns |     255.520 ns |     25,525.67 ns |  3.11 |    0.06 |    1.4648 |   0.0916 |        - |    9376 B |
|               ImmutableDict_Add |   100 |     46,542.15 ns |     412.627 ns |     344.562 ns |     46,612.94 ns |  5.68 |    0.09 |    7.9346 |   0.3662 |        - |   49952 B |
|                                 |       |                  |                |                |                  |       |         |           |          |          |           |
|        V4_ImHashMap_AddOrUpdate |  1000 |    152,860.18 ns |   1,517.703 ns |   1,345.404 ns |    152,745.43 ns |  1.00 |    0.00 |   46.6309 |   0.4883 |        - |  293656 B |
|            V2_ImMap_AddOrUpdate |  1000 |    198,915.64 ns |   2,889.932 ns |   2,561.850 ns |    198,557.64 ns |  1.30 |    0.02 |   84.9609 |   0.2441 |        - |  534144 B |
| V4_PartitionedImMap_AddOrUpdate |  1000 |     83,983.62 ns |   1,391.788 ns |   1,301.880 ns |     83,699.54 ns |  0.55 |    0.01 |   27.0996 |   9.0332 |        - |  170456 B |
|       DictSlim_GetOrAddValueRef |  1000 |     26,659.61 ns |     349.284 ns |     326.721 ns |     26,615.57 ns |  0.17 |    0.00 |   11.6272 |   2.8992 |        - |   73120 B |
|                     Dict_TryAdd |  1000 |     31,317.33 ns |     475.471 ns |     444.756 ns |     31,251.40 ns |  0.21 |    0.00 |   21.2402 |   0.0610 |        - |  133896 B |
|           ConcurrentDict_TryAdd |  1000 |    112,582.19 ns |   1,221.657 ns |   1,082.967 ns |    112,203.70 ns |  0.74 |    0.01 |   32.7148 |   0.1221 |        - |  205368 B |
|       ImmutableDict_Builder_Add |  1000 |    350,888.85 ns |   3,757.786 ns |   3,515.035 ns |    352,417.77 ns |  2.30 |    0.03 |   15.1367 |   4.8828 |        - |   95776 B |
|               ImmutableDict_Add |  1000 |    692,782.78 ns |   5,756.492 ns |   5,102.980 ns |    694,477.10 ns |  4.53 |    0.05 |  112.3047 |   0.9766 |        - |  710209 B |
|                                 |       |                  |                |                |                  |       |         |           |          |          |           |
|        V4_ImHashMap_AddOrUpdate | 10000 |  3,879,586.59 ns |  64,823.212 ns |  60,635.673 ns |  3,882,537.11 ns |  1.00 |    0.00 |  632.8125 | 312.5000 |  46.8750 | 3993786 B |
|            V2_ImMap_AddOrUpdate | 10000 |  4,485,663.73 ns |  54,179.233 ns |  45,242.113 ns |  4,483,992.58 ns |  1.16 |    0.02 | 1109.3750 | 226.5625 | 101.5625 | 6972711 B |
| V4_PartitionedImMap_AddOrUpdate | 10000 |  2,822,478.66 ns |  49,570.016 ns |  85,505.842 ns |  2,806,964.45 ns |  0.73 |    0.04 |  433.5938 | 214.8438 |        - | 2720602 B |
|       DictSlim_GetOrAddValueRef | 10000 |    424,813.34 ns |   2,027.361 ns |   1,797.203 ns |    424,378.52 ns |  0.11 |    0.00 |  124.5117 | 124.5117 | 124.5117 |  975754 B |
|                     Dict_TryAdd | 10000 |    526,320.80 ns |   9,338.940 ns |   8,278.727 ns |    523,071.63 ns |  0.14 |    0.00 |  221.6797 | 221.6797 | 221.6797 | 1261763 B |
|           ConcurrentDict_TryAdd | 10000 |  2,721,195.59 ns |  62,415.534 ns | 182,069.041 ns |  2,805,224.80 ns |  0.72 |    0.04 |  273.4375 | 121.0938 |  42.9688 | 1645328 B |
|       ImmutableDict_Builder_Add | 10000 |  4,653,773.55 ns |  48,265.920 ns |  42,786.481 ns |  4,645,701.95 ns |  1.20 |    0.02 |  148.4375 |  70.3125 |        - |  959781 B |
|               ImmutableDict_Add | 10000 | 10,911,107.09 ns | 101,847.861 ns |  85,047.577 ns | 10,956,526.56 ns |  2.81 |    0.04 | 1468.7500 | 265.6250 | 125.0000 | 9271220 B |

Lookup

The benchmark lookups for the last added index in the ImHashMap<int, string> containing the specified Count of elements.

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                        Method | Count |       Mean |     Error |    StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|------------------------------ |------ |-----------:|----------:|----------:|------:|--------:|------:|------:|------:|----------:|
|          V4_ImHashMap_TryFind |     1 |  2.5662 ns | 0.0840 ns | 0.0701 ns |  1.00 |    0.00 |     - |     - |     - |         - |
| V4_PartitionedHashMap_TryFind |     1 |  2.9264 ns | 0.0775 ns | 0.0687 ns |  1.14 |    0.03 |     - |     - |     - |         - |
|              V2_ImMap_TryFind |     1 |  0.8574 ns | 0.0826 ns | 0.0772 ns |  0.33 |    0.02 |     - |     - |     - |         - |
|          DictSlim_TryGetValue |     1 |  3.7989 ns | 0.1118 ns | 0.1046 ns |  1.48 |    0.05 |     - |     - |     - |         - |
|              Dict_TryGetValue |     1 |  7.5973 ns | 0.2095 ns | 0.1857 ns |  2.95 |    0.08 |     - |     - |     - |         - |
|    ConcurrentDict_TryGetValue |     1 |  8.1365 ns | 0.1859 ns | 0.1552 ns |  3.17 |    0.08 |     - |     - |     - |         - |
|     ImmutableDict_TryGetValue |     1 | 15.7728 ns | 0.3912 ns | 0.4348 ns |  6.16 |    0.25 |     - |     - |     - |         - |
|                               |       |            |           |           |       |         |       |       |       |           |
|          V4_ImHashMap_TryFind |    10 |  3.0618 ns | 0.0535 ns | 0.0474 ns |  1.00 |    0.00 |     - |     - |     - |         - |
| V4_PartitionedHashMap_TryFind |    10 |  2.5114 ns | 0.1019 ns | 0.0851 ns |  0.82 |    0.02 |     - |     - |     - |         - |
|              V2_ImMap_TryFind |    10 |  3.5793 ns | 0.1092 ns | 0.1022 ns |  1.17 |    0.04 |     - |     - |     - |         - |
|          DictSlim_TryGetValue |    10 |  4.0213 ns | 0.0329 ns | 0.0275 ns |  1.31 |    0.02 |     - |     - |     - |         - |
|              Dict_TryGetValue |    10 |  6.9583 ns | 0.0809 ns | 0.0717 ns |  2.27 |    0.03 |     - |     - |     - |         - |
|    ConcurrentDict_TryGetValue |    10 |  7.9926 ns | 0.0997 ns | 0.0884 ns |  2.61 |    0.05 |     - |     - |     - |         - |
|     ImmutableDict_TryGetValue |    10 | 17.5147 ns | 0.3430 ns | 0.3209 ns |  5.72 |    0.15 |     - |     - |     - |         - |
|                               |       |            |           |           |       |         |       |       |       |           |
|          V4_ImHashMap_TryFind |   100 |  6.9090 ns | 0.1161 ns | 0.1030 ns |  1.00 |    0.00 |     - |     - |     - |         - |
| V4_PartitionedHashMap_TryFind |   100 |  2.6762 ns | 0.0542 ns | 0.1045 ns |  0.39 |    0.02 |     - |     - |     - |         - |
|              V2_ImMap_TryFind |   100 |  7.1365 ns | 0.1727 ns | 0.1442 ns |  1.03 |    0.03 |     - |     - |     - |         - |
|          DictSlim_TryGetValue |   100 |  4.4196 ns | 0.0861 ns | 0.0719 ns |  0.64 |    0.01 |     - |     - |     - |         - |
|              Dict_TryGetValue |   100 |  7.6746 ns | 0.0770 ns | 0.0643 ns |  1.11 |    0.02 |     - |     - |     - |         - |
|    ConcurrentDict_TryGetValue |   100 |  8.0521 ns | 0.1363 ns | 0.1138 ns |  1.17 |    0.03 |     - |     - |     - |         - |
|     ImmutableDict_TryGetValue |   100 | 19.5683 ns | 0.1622 ns | 0.1355 ns |  2.83 |    0.04 |     - |     - |     - |         - |
|                               |       |            |           |           |       |         |       |       |       |           |
|          V4_ImHashMap_TryFind |  1000 | 12.7430 ns | 0.2270 ns | 0.2123 ns |  1.00 |    0.00 |     - |     - |     - |         - |
| V4_PartitionedHashMap_TryFind |  1000 |  7.0856 ns | 0.0987 ns | 0.0824 ns |  0.55 |    0.01 |     - |     - |     - |         - |
|              V2_ImMap_TryFind |  1000 | 10.9892 ns | 0.2986 ns | 0.3067 ns |  0.86 |    0.02 |     - |     - |     - |         - |
|          DictSlim_TryGetValue |  1000 |  4.3216 ns | 0.1560 ns | 0.1459 ns |  0.34 |    0.01 |     - |     - |     - |         - |
|              Dict_TryGetValue |  1000 |  7.9061 ns | 0.1667 ns | 0.1478 ns |  0.62 |    0.02 |     - |     - |     - |         - |
|    ConcurrentDict_TryGetValue |  1000 |  8.1644 ns | 0.1095 ns | 0.0914 ns |  0.64 |    0.02 |     - |     - |     - |         - |
|     ImmutableDict_TryGetValue |  1000 | 22.1566 ns | 0.2936 ns | 0.2603 ns |  1.74 |    0.03 |     - |     - |     - |         - |
|                               |       |            |           |           |       |         |       |       |       |           |
|          V4_ImHashMap_TryFind | 10000 | 17.4170 ns | 0.2906 ns | 0.2576 ns |  1.00 |    0.00 |     - |     - |     - |         - |
| V4_PartitionedHashMap_TryFind | 10000 | 11.0928 ns | 0.1834 ns | 0.1626 ns |  0.64 |    0.01 |     - |     - |     - |         - |
|              V2_ImMap_TryFind | 10000 | 15.6074 ns | 0.2325 ns | 0.2175 ns |  0.90 |    0.02 |     - |     - |     - |         - |
|          DictSlim_TryGetValue | 10000 |  4.4326 ns | 0.1312 ns | 0.1228 ns |  0.25 |    0.01 |     - |     - |     - |         - |
|              Dict_TryGetValue | 10000 |  7.5615 ns | 0.0669 ns | 0.0559 ns |  0.43 |    0.01 |     - |     - |     - |         - |
|    ConcurrentDict_TryGetValue | 10000 |  7.5147 ns | 0.1537 ns | 0.1437 ns |  0.43 |    0.01 |     - |     - |     - |         - |
|     ImmutableDict_TryGetValue | 10000 | 37.8435 ns | 0.4362 ns | 0.4080 ns |  2.17 |    0.04 |     - |     - |     - |         - |

Interpreting results: ImHashMap holds very good against ImmutableDictionary sibling and even against Dictionary(s) (especially if we are talking about PartitionedImHashMap) up to certain count, indicating that immutable collection could be quite fast for lookups.

Enumeration

The benchmark source code

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i9-8950HK CPU 2.90GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=6.0.202
  [Host]     : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT
  DefaultJob : .NET Core 6.0.4 (CoreCLR 6.0.422.16404, CoreFX 6.0.422.16404), X64 RyuJIT

|                        Method | Count |          Mean |        Error |        StdDev | Ratio | RatioSD |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|------------------------------ |------ |--------------:|-------------:|--------------:|------:|--------:|-------:|------:|------:|----------:|
|            V4_HashMap_foreach |     1 |      39.92 ns |     0.820 ns |      0.767 ns |  1.00 |    0.00 |      - |     - |     - |         - |
| V4_PartitionedHashMap_foreach |     1 |     116.81 ns |     1.450 ns |      1.286 ns |  2.93 |    0.06 |      - |     - |     - |         - |
|            V2_ImMap_Enumerate |     1 |      23.93 ns |     0.346 ns |      0.306 ns |  0.60 |    0.01 | 0.0114 |     - |     - |      72 B |
|              DictSlim_foreach |     1 |      12.08 ns |     0.160 ns |      0.133 ns |  0.30 |    0.01 |      - |     - |     - |         - |
|                  Dict_foreach |     1 |      13.23 ns |     0.221 ns |      0.185 ns |  0.33 |    0.01 |      - |     - |     - |         - |
|        ConcurrentDict_foreach |     1 |     160.56 ns |     1.083 ns |      0.960 ns |  4.02 |    0.07 | 0.0100 |     - |     - |      64 B |
|         ImmutableDict_foreach |     1 |     162.69 ns |     2.671 ns |      2.367 ns |  4.08 |    0.09 |      - |     - |     - |         - |
|                               |       |               |              |               |       |         |        |       |       |           |
|            V4_HashMap_foreach |    10 |     153.45 ns |     0.997 ns |      0.884 ns |  1.00 |    0.00 |      - |     - |     - |         - |
| V4_PartitionedHashMap_foreach |    10 |     404.07 ns |     3.534 ns |      3.133 ns |  2.63 |    0.02 |      - |     - |     - |         - |
|            V2_ImMap_Enumerate |    10 |     122.57 ns |     2.177 ns |      1.700 ns |  0.80 |    0.01 | 0.0176 |     - |     - |     112 B |
|              DictSlim_foreach |    10 |      53.15 ns |     0.771 ns |      0.721 ns |  0.35 |    0.01 |      - |     - |     - |         - |
|                  Dict_foreach |    10 |      51.03 ns |     0.977 ns |      0.816 ns |  0.33 |    0.01 |      - |     - |     - |         - |
|        ConcurrentDict_foreach |    10 |     282.17 ns |     4.126 ns |      3.860 ns |  1.84 |    0.03 | 0.0100 |     - |     - |      64 B |
|         ImmutableDict_foreach |    10 |     554.93 ns |     7.623 ns |      6.758 ns |  3.62 |    0.05 |      - |     - |     - |         - |
|                               |       |               |              |               |       |         |        |       |       |           |
|            V4_HashMap_foreach |   100 |   1,620.36 ns |    15.329 ns |     12.801 ns |  1.00 |    0.00 |      - |     - |     - |         - |
| V4_PartitionedHashMap_foreach |   100 |   1,966.77 ns |    26.880 ns |     25.144 ns |  1.21 |    0.02 |      - |     - |     - |         - |
|            V2_ImMap_Enumerate |   100 |   1,148.46 ns |    12.437 ns |     11.025 ns |  0.71 |    0.01 | 0.0210 |     - |     - |     136 B |
|              DictSlim_foreach |   100 |     529.39 ns |     5.573 ns |      4.940 ns |  0.33 |    0.00 |      - |     - |     - |         - |
|                  Dict_foreach |   100 |     494.13 ns |     9.209 ns |      8.614 ns |  0.31 |    0.01 |      - |     - |     - |         - |
|        ConcurrentDict_foreach |   100 |   2,370.15 ns |    33.237 ns |     31.090 ns |  1.46 |    0.02 | 0.0076 |     - |     - |      64 B |
|         ImmutableDict_foreach |   100 |   4,524.35 ns |    40.547 ns |     33.858 ns |  2.79 |    0.03 |      - |     - |     - |         - |
|                               |       |               |              |               |       |         |        |       |       |           |
|            V4_HashMap_foreach |  1000 |  17,206.01 ns |   152.714 ns |    135.377 ns |  1.00 |    0.00 |      - |     - |     - |         - |
| V4_PartitionedHashMap_foreach |  1000 |  21,030.80 ns |   325.220 ns |    288.299 ns |  1.22 |    0.02 |      - |     - |     - |         - |
|            V2_ImMap_Enumerate |  1000 |  12,200.97 ns |   173.829 ns |    162.600 ns |  0.71 |    0.01 | 0.0153 |     - |     - |     160 B |
|              DictSlim_foreach |  1000 |   4,913.65 ns |    76.788 ns |     71.827 ns |  0.29 |    0.00 |      - |     - |     - |         - |
|                  Dict_foreach |  1000 |   4,963.77 ns |    69.813 ns |     65.303 ns |  0.29 |    0.00 |      - |     - |     - |         - |
|        ConcurrentDict_foreach |  1000 |  21,569.87 ns |   162.467 ns |    144.023 ns |  1.25 |    0.01 |      - |     - |     - |      64 B |
|         ImmutableDict_foreach |  1000 |  47,263.06 ns |   907.028 ns |    804.057 ns |  2.75 |    0.05 |      - |     - |     - |         - |
|                               |       |               |              |               |       |         |        |       |       |           |
|            V4_HashMap_foreach | 10000 | 182,837.99 ns | 2,052.717 ns |  1,819.680 ns |  1.00 |    0.00 |      - |     - |     - |     176 B |
| V4_PartitionedHashMap_foreach | 10000 | 232,269.89 ns | 2,514.057 ns |  2,099.352 ns |  1.27 |    0.02 |      - |     - |     - |         - |
|            V2_ImMap_Enumerate | 10000 | 138,194.71 ns | 1,605.065 ns |  1,340.302 ns |  0.76 |    0.01 |      - |     - |     - |     192 B |
|              DictSlim_foreach | 10000 |  49,479.00 ns |   937.417 ns |  1,003.025 ns |  0.27 |    0.00 |      - |     - |     - |         - |
|                  Dict_foreach | 10000 |  46,780.99 ns |   380.189 ns |    355.629 ns |  0.26 |    0.00 |      - |     - |     - |         - |
|        ConcurrentDict_foreach | 10000 | 194,166.07 ns |   919.960 ns |    860.531 ns |  1.06 |    0.01 |      - |     - |     - |      64 B |
|         ImmutableDict_foreach | 10000 | 507,513.23 ns | 9,995.314 ns | 12,640.872 ns |  2.80 |    0.07 |      - |     - |     - |       1 B |
****```


## End-to-end Example

Let's assume you are implementing yet another DI container because why not :-)

Container should contain registry of `Type` to `Factory` mappings. 
On resolution `Factory` is compiled to the delegate which you would like to cache, because compilation is costly. 
The cache will store the mappings from `Type` to `Func<object>`.

__The requirements:__

- The container may be used in parallel from different threads including registrations and resolutions. 
- The container state should not be corrupted and the cache should correspond to the current state of registrations.

Let's design the basic container structure to support the requirements and __without locking__:

```cs
    public class Container
    {
        private readonly Ref<Registry> _registry = Ref.Of(new Registry());

        public void Register<TService, TImpl>() where TImpl : TService, new()
        {
            _registry.Swap(reg => reg.With(typeof(TService), new Factory(typeof(TImpl))));
        }

        public object Resolve<TService>()
        {
            return (TService)(_registry.Value.Resolve(typeof(TService)) ?? ThrowUnableToResolve(typeof(TService)));
        }
        
        public object ThrowUnableToResolve(Type t) { throw new InvalidOperationException("Unable to resolve: " + t); }

        class Registry 
        {
            ImHashMap<Type, Factory> _registrations = ImHashMap<Type, Factory>.Empty;
            Ref<ImHashMap<Type, Func<object>>> _resolutionCache = Ref.Of(ImHashMap<Type, Func<object>>.Empty);

            // Creating a new registry with +1 registration and new reference to cache value
            public Registry With(Type serviceType, Factory implFactory)
            {
                return new Registry() 
                {	
                    _registrations = _registrations.AddOrUpdate(serviceType, implFactory),
                        
                    // Here is most interesting part:
                    // We are creating new independent reference pointing to cache value,
                    // isolating it from possible parallel resolutions, 
                    // which will swap older version/ref of cache and won't touch the new one.
                    _resolutionCache = Ref.Of(_resolutionCache.Value)
                };
            }

            public object Resolve(Type serviceType)
            {
                var func = _resolutionCache.Value.GetValueOrDefault(serviceType);
                if (func != null)
                    return func();

                var reg = _registrations.GetValueOrDefault(serviceType);
                if (reg == null)
                    return null;
                
                func = reg.CompileDelegate();
                _resolutionCache.Swap(cache => cache.AddOrUpdate(serviceType, func));
                return func.Invoke();
            }
        }
        
        class Factory 
        {
            public readonly Type ImplType;
            public Factory(Type implType) { ImplType = implType; }
            public Func<object> CompileDelegate() { return () => Activator.CreateInstance(ImplType); }
        } 
    }