Analyzer to flag a non-public class if it is not marked as sealed

[alrz]

No description provided.

[benaadams]

Only relevant if it has override methods?

[alrz]

@benaadams

Why? In my experience, sealed types generally have better isinst performance so I think this should be applied regardless of the presence of overridden methods. This is, however, only relevant if it hasn't any derived classes.

Further, we could use an option to produce warning if (public) types are not explicitly marked as non-sealed (with an attribute).

[benaadams]

Further, we could use an option to produce warning if (public) types are not explicitly as non-sealed (with an attribute).

Basically you are saying classes should always be sealed by default?

Non-sealed classes are very useful to side-car data which you can't do with composition; e.g. pass type to api, which then api passes elsewhere to get the data back out - without creating a global(ish) dictionary on with the object as key.

sealed types generally have better isinst performance

If you are using isinst its a direct example of side-carring data on the object type (or the type's parent/hierarchy)

[alrz]

Basically you are saying classes should always be sealed by default?

This is what I'm trying to say:

private class HasNoDerivedTypes {} // warning: the type can be sealed

public class HasNoDerivedTypes {} // optional warning
[NonSealed] public class HasNoDerivedTypes {} // explicit suppression 

Note: this is an IDE request.

[CyrusNajmabadi]

I see. It sounds like you want a suggestion that says to mark a class as sealed iff:

1. it has private accessibility.
2. it is not subclassed within the assembly.

If so, that seems reasonable. Sounds like it would go in the roslyn-analyzers repo though.

Note: afaict, there is no way to do this with the current analyzer system. You'd need a CompilationEndAction so you could ensure that there were no subclasses. But CompilationEndActions do not run by defualt for users. Tagging @heejaechang

[jinujoseph]

Tagging @mavasani , @dotnet/roslyn-analysis

[Youssef1313]

Duplicate of dotnet/runtime#49944

This analyzer will be implemented in dotnet/roslyn-analyzers repository, except for the "optional warning" part for public APIs. This is very unlikely to be useful.

@jinujoseph I believe this issue can be closed.