CS0465 description doesn't match behavior

[GeeLaw]

Type of issue

Outdated article

Description

CS0465 documentation says:

This warning occurs when you create a class with a method whose signature is public virtual void Finalize.

If such a class is used as a base class and if the deriving class defines a finalizer, the finalizer will override the base class Finalize method, not Finalize.

However, currently (used from VS 18.9.1 on Windows 11 x64, targeting .NET 10 AnyCPU), the actual behavior is different.

• The warning is (IMO correctly) emitted for all accessibility modifiers (except private, which C# anyway doesn't allow for virtual methods).
• Suppose B introduces protected virtual void Finalize() { } (new slot).
• Suppose D : B defines a finalizer ~D() { }.

The effect is as follows:

• D's finalizer overrides both B.Finalize and object.Finalize. The C# compiler emits explicit .override object::Finalize() in D's synthesized Finalize, so it does override object.Finalize. The method is also non-newslot and virtual, so it overrides B.Finalize due to matching name and signature.
• D's finalizer will call instance B.Finalize, which is, of course, not the finalizer (I take "finalizer" to mean the override of object.Finalize).

More interestingly, if B.Finalize is...

• public or internal or protected internal, then type D fails to load (override cannot reduce access);
• private protected, then D.Finalize overrides B.Finalize and object.Finalize, and in D.Finalize, it calls object.Finalize not B.Finalize (this happens even if B.Finalize is accessible to D);
• non-virtual but protected or protected internal, then D.Finalize will call B.Finalize (and not object.Finalize), but of course only overrides object.Finalize.

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Maybe the documentation was accurate for some versions of C# compiler. I suspect the situation is simply unsupported as defining a method called Finalize (except via the finalizer syntax) is anyway a very bad idea. If both are true, I suggest avoiding describing what happens when one defines such a method, and simply say "doing so interferes with finalization logic".

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/cs0465?f1url=%3FappId%3Droslyn%26k%3Dk(CS0465)

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/language-reference/compiler-messages/cs0465.md

Document Version Independent Id

53f17a1d-75c8-7fe6-1b0c-7893ae6fc0c4

Platform Id

ac53118f-3da2-cf27-577d-9745af24231b

Article author

@BillWagner

Metadata

• ID: 93138196-598c-7726-1b74-4cb6e4b302a3
• PlatformId: ac53118f-3da2-cf27-577d-9745af24231b
• Service: dotnet-csharp
• Sub-service: errors-warnings

Related Issues

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Associated WorkItem - 627639

[adegeo]

Hello. I'm trying to understand what specifically you're requesting be changed on the page. Is the problem that it says

This warning occurs when you create a class with a method whose signature is public virtual void Finalize.

Which really isn't true, it's any method named Finalize on an object that triggers the warning.

[GeeLaw]

If such a class is used as a base class and if the deriving class defines a finalizer, the finalizer will override the base class Finalize method, not Finalize.

This description is incorrect. The actual behavior is (partially?) described in the issue description, and it's quite complex.

Is the problem that it says

This warning occurs when you create a class with a method whose signature is public virtual void Finalize.

Which really isn't true, it's any method named Finalize on an object that triggers the warning.

That's a good catch. The warning is triggered by any method with signature void Finalize(), regardless of virtuality or accessibility modifier.

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what specifically you're requesting be changed on the page

The information shown on the page is very different from the actual behavior, so there's no "specific thing to be changed". Rather, it should be rewritten from scratch. One suggested version:

Introducing a 'Finalize' method can interfere with finalization. Did you intend to declare a finalizer?

This warning occurs when you create a type with a method of signature void Finalize().

The finalizer is protected virtual void Finalize() on System.Object. Since members are matched by name and signature, their collision with the finalizer could lead to mix-up of overrides and incorrect finalization logic. If you intended to declare a finalizer, use ~ClassName() syntax; otherwise, rename the method to avoid collision.

The changes:

1. destructor => finalizer.
2. class => type (this warning is shown also in struct and interface).
3. Remove public virtual since it's not a necessary condition.
4. Change the last paragraph to be correct without going into the crazy details, while providing some hint on why the issue appears.
5. Add suggested action.