Unable to override SearchValues

[JanTamis]

Is there a reason SearchValues cant be overridden?

[huoyaoyuan]

It uses highly specialized algorithms based on the exact input values. The public Contains method is just a fallback.

[MihaZupan]

Yes, providing different implementations is intentionally restricted to .NET (CoreLib) itself.
This allows us to evolve the type easier without having to think about whether adding new APIs will break something for custom implementations.

If someone has better ideas around how something can be implemented, or more patterns we should consider special-casing, we're happy to consider including them into .NET itself.
Did you have anything like that in mind / why did you wish to override it?

In such cases the user also shouldn't be blocked by the lack of extensibility as a more specialized IndexOfAny-like implementation can easily live as an extenion method in user code.

[JanTamis]

I'm trying to make a ConstExpr source generator that can generate a custom implementation of SearchValues if a custom interfaces implmements this.

[MihaZupan]

What are the sorts of things you ran into that make that a better option than using the existing SearchValues.Create? Are you looking at startup perf / different algorithms / different ways to initialize sets of values?
If you have ideas for different implementation strategies that outperform the built-in ones, we'd love to hear about it and see if it may apply to more use cases.