.NET 8 performance: 10x faster GetGenericTypeDefinition

.NET 8 brings some neat performance improvements for existing APIs that handle type information. One such API that has seen a significant improvement is GetGenericTypeDefinition.

In my benchmarks, the .NET 8 implementation is almost 10 times faster compared to the .NET 7 version.

| Method                   | Runtime  | Mean      | Error     | StdDev    |
|------------------------- |--------- |----------:|----------:|----------:|
| GetGenericTypeDefinition | .NET 7.0 | 13.078 ns | 0.0505 ns | 0.0422 ns |
| GetGenericTypeDefinition | .NET 8.0 |  1.611 ns | 0.0091 ns | 0.0076 ns |

You can run this benchmark yourself if you’d like using BenchmarkDotNet:

[SimpleJob(RuntimeMoniker.Net70)]
[SimpleJob(RuntimeMoniker.Net80)]
public class Benchmarks
{
    private readonly Type _type = typeof(List<int>);

    [Benchmark]
    public Type GetGenericTypeDefinition() => _type.GetGenericTypeDefinition();
}

BenchmarkRunner.Run<Benchmarks>();

Or if you’re looking for a ready-to-run sample, you can clone this repository and run the GetGenericTypeDefinitionBenchmarks.