list-empty-return

🌳 Sustainable Code - the cost of returning an empty collection

The return of empty collections is practically part of every code. But which variants cost how much - and wouldn't zero be even better?

🔥 Benchmark

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4651/22H2/2022Update)
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 9.0.100-preview.5.24307.3
  [Host]   : .NET 9.0.0 (9.0.24.30607), X64 RyuJIT AVX2
  .NET 9.0 : .NET 9.0.0 (9.0.24.30607), X64 RyuJIT AVX2

| Method      | Mean      | Ratio | Gen0   | Allocated |
|------------ |----------:|------:|-------:|----------:|
| List()      | 2.7975 ns |  1.00 | 0.0019 |      32 B |
| List(0)     | 2.9224 ns |  1.04 | 0.0019 |      32 B |
| List []     | 2.7643 ns |  0.99 | 0.0019 |      32 B |
| Array.Empty | 0.4912 ns |  0.18 |      - |         - |
| Array []    | 0.4835 ns |  0.18 |      - |         - |
| HashSet()   | 4.0250 ns |  1.48 | 0.0038 |      64 B |
| HashSet []  | 4.0798 ns |  1.46 | 0.0038 |      64 B |

🏁 Remarks

• The new notation [] is an alias for all collections in order to create the collection in the most efficient way
• The return of Array.Empty is by far the fastest and most efficient way; the array is only created once in the background and then statically retained. This is not possible with other collections.

Conclusion

It is very useful to follow the current recommendation and use [].

⌨️ Run this sample

dotnet run -c Release