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🌳 Sustainable Code - Create Empty Collections 📊

A small example of how an empty collection can be created efficiently.

Docs:

🔥 Benchmark

BenchmarkDotNet v0.14.0, Windows 10 (10.0.19045.5131/22H2/2022Update)
AMD Ryzen 9 9950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 9.0.100
  [Host]   : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  .NET 7.0 : .NET 7.0.20 (7.0.2024.26716), X64 RyuJIT AVX2
  .NET 8.0 : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  .NET 9.0 : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI


| Method          | Runtime  | Mean     | StdDev    | Ratio | RatioSD | Gen0   | Allocated | Alloc Ratio |
|---------------- |--------- |---------:|----------:|------:|--------:|-------:|----------:|------------:|
| List            | .NET 7.0 | 9.466 ns | 0.1372 ns |  2.20 |    0.05 | 0.0043 |      72 B |        2.25 |
| List            | .NET 8.0 | 6.700 ns | 0.0149 ns |  1.56 |    0.02 | 0.0019 |      32 B |        1.00 |
| List            | .NET 9.0 | 4.309 ns | 0.0699 ns |  1.00 |    0.02 | 0.0019 |      32 B |        1.00 |
|                 |          |          |           |       |         |        |           |             |
| Array           | .NET 7.0 | 6.641 ns | 0.0951 ns |  1.62 |    0.03 | 0.0014 |      24 B |        1.00 |
| Array           | .NET 8.0 | 5.121 ns | 0.0530 ns |  1.25 |    0.02 | 0.0014 |      24 B |        1.00 |
| Array           | .NET 9.0 | 4.089 ns | 0.0311 ns |  1.00 |    0.01 | 0.0014 |      24 B |        1.00 |
|                 |          |          |           |       |         |        |           |             |
| ArrayEmpty      | .NET 7.0 | 4.849 ns | 0.0388 ns |  1.84 |    0.01 |      - |         - |          NA |
| ArrayEmpty      | .NET 8.0 | 3.863 ns | 0.0064 ns |  1.47 |    0.00 |      - |         - |          NA |
| ArrayEmpty      | .NET 9.0 | 2.630 ns | 0.0031 ns |  1.00 |    0.00 |      - |         - |          NA |
|                 |          |          |           |       |         |        |           |             |
| EnumerableEmpty | .NET 7.0 | 2.958 ns | 0.0069 ns |  1.13 |    0.00 |      - |         - |          NA |
| EnumerableEmpty | .NET 8.0 | 1.317 ns | 0.0066 ns |  0.50 |    0.00 |      - |         - |          NA |
| EnumerableEmpty | .NET 9.0 | 2.623 ns | 0.0067 ns |  1.00 |    0.00 |      - |         - |          NA |

🏁 Results

  • 🚀 The most efficient way to create an empty collection is Enumerable.Empty. Here no allocation is necessary, because no object is created.

Remarks

  • If you need an empty collection, it is best to work with Array.Empty or Enumerable.Empty.
  • You can use Array.Empty for all array-based collections (like ICollection), which has the same static object implementation like Enumerable.Empty.
  • All use cases became significantly faster in .NET 8, with the List case also seeing a reduction in allocation.

⌨️ Run this sample

dotnet run -c Release --framework net9.0

Updates

  • 2023/11 - Add .NET 8
  • 2024/11 - Add .NET 9